Well, the comment about clothing was sarcasm. And dryads don't wear animal clothing because they are forest spirits and don't need clothes. Archers don't wear them to blend in with the background; seeing deer antlers on a tree, it's unlikely anyone would think it's a deer and not an elf. As for the animal skins on druids, the artists probably messed up; they likely didn't know what to add to the druids to make them stand out from the others, and they ran out of ideas. :(