I mean, if the corpse is still animated, it's not a corpse but, indeed, a zombie. And nah, it doesn't count toward the fetish. Necrophilia inheres to inanimated corpses - a key part of the necrophiliac power fantasy is that the body doesn't move, and you can play with it the way you like, moving it around like a doll, dressing/undressing it, carrying it around, etc.
But if it still walks on its own, resists, and/or plays a somewhat active part in the sexual act, then it being "technically dead" by lore is irrelevant.
That's like tagging "loli" a game or hentai with a 10-year-old character, except said character is depicted as being 1.7m tall, has an F cup, a huge ass, and just got a Ph.D. in astrophysics. At that point, for you to say: "hey, technically, she's only 10 by lore!" won't work, will it? It will just sound ridiculous and preposterous - like the "necro" tag on a zombie game.
Take note, you future necro-tagged game devs/posters.