I'm assuming you're specifically talking about Call of the Dead, and not the entire storyline itself. Since y'know, you're talking about George Romero and all.
In the intro, the cast makes it clear that it's no longer being a movie. The weapons are all real in the cutscene, with the shotgun Rooker had was probably just flare-esque munition. Romero becomes what he [theoretically] is filled with both Element 115 and vril energy; hence why he cannot die and has a strange transition between human form and zombie form, unlike anything we've come across. On top of that, he can recall his memories of the cast and even communicates like normal, except with a booming voice.