I don't know why, but my tablet works in GIMP now! Sure, I'd tried again to get it to acknowledge the pressure, but it kept blanking the settings, looking like it didn't take. Today I went to see if I could use the switch or set a key to act like the mouse button so I could at least use it without the pressure-sensitivity, but instead, it worked!
Also, I think I understand why so many artists use the smudge tool so much (even sometimes when it doesn't look right), it's so much fun! After I found out I could use the tablet, I took the scribble I'd used to test out it's response, and just
smudged up the whole thing. I don't think I'd ever used a smudge too with a tablet before, it works so nicely! I think I'm gonna have to draw some fire or something just to use it.