So, I just discovered 珍珠丸子, or pearl meatballs, which have glutinous rice on the outside (and sound kind of tasty). There's a recipe here and another recipe including photos here — do those seem to have the sort of texture you're talking about? (I also found another rather peculiar-looking recipe that wants you to put at least 1 cup of water in the ground meat for the meatballs... I have no idea how that could possibly work.)

I'm actually having trouble remembering the texture of the meatballs I've had in hotpot (and those were 丸 with no 子), though I do remember the fishballs had a very homogeneous texture. Luckily I'm having hotpot tomorrow night so can check :)