Actually, there are very few non-humans, aren't there? Hagrid, Griphook, Firenze, the ghosts, and arguably Flitwick *g* But no, I think I'm making an executive decision where house elves and full giants are concerned, at least for the time being.
Mind you, there's absolutely nothing in the rules saying you can't ask that your artist/writer give you a story featuring one of them as the *other* side of the pairing (although remember the givers aren't required to fulfill secondary requests).
(still trying to come up with a good scenario for Walton/Creature that isn't crack...)