Possible to Skin in GIMP and Blender?

Is it?

It depends. To skin a Warcraft III model (what you might want to since you're posting here), you would need to convert the model from 3dsmax file-format to blender, but to my knowledge GIMP works in skinning. I would tell you to use only GIMP, since probably converting from War3 format > 3dsmax format > blender format might get weird and unexpected results, believe me. But about GIMP, I think it works, didn't try yet (I use it only on my old computer that has RedHat linux, and I didn't try to skin anything there).