Apparently, at least, according to DeviantArt, it's okay to copy a plethora of images
and allow others to assume that they're your own original pieces of art.
DA states in their ToS that this is acceptable for fan art. Whether or not DA supports mild cases of art theft; it's still ethically disgusting. What's even worse is the culprit will block anyone from commenting if they call him out, and hides their comments as spam.
I reported him some time ago, and DA told me (four months later) that it's acceptable. I'm sure if I were to re-draw another Deviant's images, though, DA would be on my ass like a fat kid on a cupcake.