I'm not exactly sure what you mean (I'll have to see the map when I get on my computer with SC.), but if you're going to edit the Marine death, its made up of two parts (the exploding part, which is frames in the marine GRP, and the blood spatter that fades away (which is a separate sprite).
No, the complete marine death anim is in its GRP. He's just saying he won't remove the corpse sprite so that dead marines stay behind forever. The only problem is you have to worry about hitting the sprite limit.