I haven't really made it a secret, my dislike for Hush Beyond (aka the 2010 6 part Batman Beyond miniseries, for those who don't know the Official Name), nor have I been shy in saying that it is not and cannot be considered canon. However, my dislike is not the reason that I say it has to be discounted as canon; saying it's not canon is merely the only reasonable response to events and timelines as portrayed in the series.
Now, HB creates a crazy mashup of comic continuity and DCAU continuity -- the events of Cataclysm (Gotham is hit by a gigantic freakin huge earthquake) and the original Hush storyline (new BM villain of "Your parents died and mine didn't! I'll kill you!"), at the very least, now apparently fit somewhere in Beyond's timeline, and the converted DCAU's backstory. I am okay with this part of it. Beyond is being transferred to a whole different medium and incorporated into a different universe, so if you wanna throw all sorts of things into the backstory, that is fine and DC's prerogative. As near as I can figure, neither of these events really mesh with the existing DCAU timeline all that well, as generally speaking those timelines are pretty tight and both Hush and Cataclysm (along with the resultant No Man's Land, if we're to believe that it follows the earthquake in this Gotham as well) are kinda major plots, but I'll buy it. Conversion to a new universe, new plots that pay homage to comic fans, fine by me. That is not the problem.
Setting aside the characterization issues, ignoring the fact that Terry's mom is the wrong race and the mysterious deaging of Jared Tate, discounting any number of much smaller errors and just letting it go as new universe stuff... it just doesn't work. In order to make the HB timeline work, you have to remove the whole thing that makes the timeline work.
First: THE JOKER.Now, in DCAU, the Joker's history ran thusly: He got created, ran around causing havoc (as the Joker will do), and then somewhere around probably 2004, he caught Tim!Robin, tortured him and drove him insane, and then was killed by him, either shot in the heart by a BANG flag or electrocuted with some liquid and live wires, depending on if you go with the edited or non-edited version of the film. Either way he is dead and is buried under Arkham. About 40 years later he mysteriously re-emerged, catching Bruce completely by surprise, and got right back to terrorizing Gotham again until he was caught and killed (again) by Terry McGinnis. Simple enough, right?
Welp, apparently DC had problems with it.
According to Hush Beyond, some years after Bruce had last had worked with a partner, the Joker was still in action. The exact line that Dick uses to establish the timeline is this: "It'd been a while since Bruce and I had worked together. He'd been working alone so long--since what happened to Silver--and he hadn't worked with a partner in years."
Now, who exactly is Silver supposed to be? I cannot remember a single instance where Bruce works with anyone either named or nicknamed Silver. I've come up with two ideas, both of which seem a little odd. Barbara Gordon might possibly be Silver, though this seems somewhat unlikely given that, despite being a silver fox in DCAU, in every issue of the comics I've seen with old!her she dyes her hair bright red. In addition, Dick calling Babs 'Silver' seems to suggest a familiarity that, while I guess I could buy, seems a little out of place in a relationship that has supposedly been estranged for about 40 years, especially as she's married to another man. Still, that's option A. The only other person who might possibly fit is Batwoman, from the movie Mystery of the Batwoman. In that film, Batwoman's batsuit is done in siver and red. However, Batwoman and Batman worked together only in the loosest sense of the word, and it'd be difficult to ever call them partners. Even saying allies is stretching it a little. Since Tim's hair has turned gray, I suppose that he is one more possibility, but it seems monumentally unlikely that he is who Dick is talking about. If you actually happen to know who Silver is, or have any ideas, drop a line and tell me cause I'm stumped.EDIT: Apparently Bruce has a love interest in the comics (he gets around, Bruce does) named Silver St. Cloud. However, I'm not entirely sure how this is relevant because: Silver is a civilian and was around during or shortly after Dick's Robin days - so long before what happened to Tim. Aka Bruce would still be working with Batgirl, and after a while, Robin. She doesn't exist afaik in DCAU canon, but since we're meshing with comics canon that isn't a huge barrier, just.
I'm not quite sure a: why she'd (apparently?) be working with Bruce, b: what the heck is supposed to have happened to her (assuming she's the Silver in question and it's not some kind of nickname for another unknown party) and c: why any of this matters anyway, as Bruce presumably fired everyone shortly after what happened to Tim, or debatably Barbara. This is the first and only time that Silver is mentioned though, so I guess we're left to wonder.
I dunno, don't ask me to make it make sense. None of this makes sense anyway.
Regardless of the actual identity of this partner who apparently had Bad Things happen to them, this event (Dick being shot full of holes by Joker) was still supposed to have taken place 'years' after Bruce worked with a partner. Now, between Dick ragequitting and Tim getting nabbed by Joker, you can maaaaaaaaybe squeeze 4 or so years out of the timeline, with creative organizing. However, between those two events, Bruce worked with Barbara, Tim, the Justice League, and the JLU. In short, the only way to make that sentence work so the time falls before the Joker died is if you assume that by 'working alone' Dick actually meant 'working with several hundred people who weren't me.' This seems... unlikely. It seems yet more unlikely because Dick was talking about fighting style, and Bruce being physically and mentally unused to fighting with someone else to look out for and work with. Whether or not the partner in question was Dick, Bruce could have been accustomed to the style of fighting with a partner if he was still fighting alongside Babs/Tim/etc. Besides that, keep in mind that Dick seems to count Silver as Bruce's partner, which discounts the whole 'no one if it's not me!' theory completely. Which means that Bruce had been working alone for years which means that he already fired everyone after Joker got Tim and was killed by him.
In short, the only way for this timeline to make any sense at all is to throw out RotJ, which makes the timeline make no sense at all, because the events of RotJ are why Bruce fired everyone to begin with! In order for the Joker to be there, the Joker already has to be dead, which means the Joker can't be there. Catch-22. This throws the entire timeline of Hush Beyond completely out of sync with canon and even out of sync with itself, as it relies on the events of RotJ at the same time that it makes them impossible.
Second: CADMUS.The entire plot of Hush Beyond mostly hinges on Amanda Waller stealing Dick's DNA and creating Dick!clones to be future Batman, then training and brainwashing them into being psycho Batman replacements. Would she do this? Yes, probably. Does it mesh with anything else? Not even slightly, no.
Amanda thinks that Gotham needs a Batman: check. Amanda is willing to genetically build her own Batman: check. After this it all falls apart.
In DCAU, Amanda Waller was the creator of something that she called Project Batman Beyond (i c wat u did thar dc), which involved stealing Bruce's DNA and using it to create Terry, who's like. A half-clone of Bruce. She does this because she appears to think that in order to be Batman, one needs to be in possession of Bruce's magicgenes and nothing else will do! So she genetically manipulates her way to a Terry, and then when he's 8 years old and leaving a theatre, she moves to kill his folks. Plans get canceled last microsecond, and his parents don't actually die, but it is a seriously close thing. So here come the problems.
Amanda ended up creating Dick!clones for her (latest) future!batman project because she felt that Bruce!clones would be too unstable because... Bruce is too unstable and shouldn't be Batman. So when Dick is shot full of holes from his run-in with the Joker and thus in the hospital, Waller runs to grab his DNA and starts using it to clone him, as trainedbyBruceDNA is an acceptable alternative to actual BruceDNA. Apparently.
The problem here is that Terry was cloned using Bruce's DNA, not Dick's DNA, and Waller keeps the project active until Terry is 8 years old. By the time Terry is 8, Bruce has already been retired for 12 years, so it's not exactly as if you can say that this is when Bruce and Dick went out and Dick got shot full of holes. And Terry was built with Bruce's DNA. If she wanted Dick's DNA and to start project new!batman that way, Terry wouldn't exist.
Basically, in order for there to be a villain in the series, you have to eliminate the hero. Whoooooops.
And then there's all the other problems with the series that are smaller or more subjective so I didn't mention them here, but that doesn't mean they're not still (occasionally significant) problems.
TL;DR: HUSH BEYOND GOT PROBLEMS AND IT DOESN'T WORK.