I doubt what everyone is thinking, it seems likely to me that moria was using corpses from the war, judging by the fact that those zombies were rising from the ice, meaning that they were either corpses from the war, or had been buried under the ice, which is impossible, as the ice was recently frozen, and the seawater before would have killed them.
It seems likely that oda just draws the zombies like that so they aren't so scary, like they would be if he were to draw mutilated corpses, just like how he avoids showing corpses in the battlefield in general, if you look at oda's commentary, its' the same with buggy, and why you can't see his blood and organs when he is cut up, he just thinks it looks less messed up. Their marine uniforms should indicate where the bodies came from, I doubt he killed marines beforehand, and don't see why he would dress them up. Moria most likely took a bunch of shadows from men in the control rooms or somewhere else indoors, and then used them there and to buff himself.
