Sorry more likely a tourted dead person than a zombie. But one can only hope

I think Ozwell or somebody else is experimenting on people
http://uk.ps3.ign.com/dor/objects/33572/resident-evil-5-alternative-edition/images/resident-evil-5-gold-edition-20091119111629249.html

Kind of like how Tricell experimented on people from all over the world in the main storyline of Resident Evil 5.

Lost in Nightmares was very short, only about an hour on Normal, although it is quite difficult on harder difficulties, to the extent I died about fourteen times in the span of half an hour against those enemies so often references, known, I believe, as the Guardians of Death or something close to that. I just call them Guardians, or Anchor Man. ^_^;

The zombies people saw were, in fact, progenitor zombies, which implies that Spencer was experimenting with the Progenitor virus in his basement and the sewers below it, and I believe the Guardians could have been there to oversee the prisoners, perhaps, or maybe they were a different strand of the Progenitor virus that mutated people in a way not quite expected? I'm not sure.

The game is definitely worth buying, though.