In BG3, I’d wager that they all use the same illithid model.
I seem to recall in Act 3 after a certain point:
Tap for spoiler
Seeing random citizens all getting transformed after having all the macguffins when I fast travelled. Gnomes and dwarves both got the tall illithid model.
Yes but also no. Ceremorphosis only truly succeeds on certain kinds of species, generally only those of the human sized variety and a few kinds of monster. Gnomes can be technically transformed but only through heavy magic manipulation and there is still a chance of failure. All others just die along with the tadpole