Answer: Reporting Clauses and the Verb "Hear"
velocitygrass asks "Can the reporting clause ever be indirect with the verb 'hear'?"
Let's take a look at the reporting clause and see if there's a good answer to this question.
First, a confession: your humble Fandom Grammarian here had never heard of the term "reporting clause" (or its partner, the "reported clause") previously. However, a bit of research showed that they are pretty straightforward:
Reporting clause Reported clause Vimes said he was sick and tired of listening to his Dis-Organizer. The Alchemists Guild claims that transmutation is possible. Angua thought that Carrot looked a bit tired for once.
Together, the reporting clause and the reported make up indirect discourse. Again, the easiest way to explain this is by example:
Direct Discourse:
"There's nothing quite like a good loaf of Dwarf bread," said Carrot.
"I imagine that's true," said Angua, after a moment.
Indirect Discourse:
Carrot said that there was nothing quite like a good loaf of Dwarf bread.
After a moment, Angua answered that she imagined that was true.
As you see, in direct discourse, the characters' words are quoted: we see exactly what the characters said. This is how we're used to seeing speech handled in fiction. In indirect discourse, the characters' words are paraphrased to one extent or another. Notice, for example, that Angua's "I imagine" has become "she imagined."
Now that we have the terminology straight, let's take another look at the question. velocitygrass is asking about using the verb "hear" in the reporting clause. I'm going to assume that what's meant is a sentence like this:
Detritus heard that werewolves didn't get along with vampires.
The interesting thing about this sentence is that it's hard to guess what the direct version would have been. From whom did Detritus hear this information? Still, even just turning the sentence around gives us a reasonable, if not exactly common, sentence:
"Werewolves didn't get along with vampires," was what Detritus heard.
A little more information might make the sentence less odd:
"Werewolves didn't get along with vampires," was what Detritus heard whenever he brought up the issue of Angua's friendship with Sally.
Both versions are legitimate English sentences, however.
In researching this question, I couldn't find any direct discussion of this situation. However, Advanced Grammar in Use (by Martin Hewings), a manual aimed at university-level students, has an extensive discussion of reporting clauses that includes this example:
I hear you're unhappy with your job.
What's interesting about this sentence is that the use of "hear" adds a level of uncertainty about the information that's reported - and that's probably deliberate. The speaker is implying that zie doesn't know whether it's true that the other person is unhappy, and zie is leaving open the question of how zie found out about the other person's supposed dissatisfaction.
With this idea in mind, let's go back to our troll watchman and the question of enmity between vampires and werewolves:
Detritus heard that werewolves didn't get along with vampires.
Now we can see that the author might have selected the verb "hear" deliberately for that element of uncertainty. Detritus might not remember exactly who told him about the animosity between vampires and werewolves, or he might have heard it several times, from several sources. It doesn't really matter: what's important is that it's an idea that doesn't come from his own experiences and that he is uncertain whether it's true or not.
So, in answer to the original question, we've found that "hear" can indeed be used in a reporting clause. It can even be a wise choice if you want to suggest that the information reported might be wrong or doesn't have a definite source.