By a strict reading they can be nominated for either, but I think the spirit of Marrow Hunger is that they clearly are going to murder/eat someone so it's your choice, but I'd call it cheese in my group.
I find that KDM loses alot when you start ignoring theme entirely in your choices in favor of what is numerically best.
Totally agree, min/maxing KD:M makes it boring in the long run. But I will also say I can totally see it working thematically both ways. The Skull Eater killing someone to feast upon them is obvious. But what if another insane survivor realized that the Skull Eater is dangerous and decided to take care of the problem before they get eaten themselves?