It's been a while since I read TORG, but I think this setting could give you an alternative reason besides time travel to mix different genres.

Romero zombies in Orrorsh
Cyber zombies in the Pope's domain
Gen Mod zombies in Nippon
Fantasy zombies and skeletons in Aysle
Mummies in the pulp Egypt pulp setting
and a zombie T-Rexx in the Living World.