1) Before the zombie plague that universe was closer to the regular Marvel U than the Ultimate one, but still it wasn't exactly like it... For example, Captain America has a different name, and there's characters that appeared after Galactus' first appareance that are there even though Galactus is making his first visit to earth in this comic.
2) It's a superhero comic AND a zombie story. Starting with that, all suspension of disbelief levels should go to hell. On top of that, in spite of the crudeness, it's an openly "fun" comic... At this point, it doesn't make any difference at all if the story is feasible or not.
