I've now wasted DDO Store cosmetic hats on the Micrometeor Swarm, Warforged Peacock, Dread Triceratops Hatchling, and the Dread Raptor Chick. Apparently none of these pets can wear cosmetics, yet there's no warning whatsoever when you go to use one on them, and you just waste your DDO points on nothing.
Some older pets like Pet Rock, and the 4 animated coin pets, at least have warnings that "You can't use that item on this pet", but this seems to have been completely forgotten on newer pets