I dont know why, but I totally forgot that this "overlay" takes over the DL HM nearly 1/2 of the year.
Zombies? No. They would be in desperate attempt to feed on the flesh of the living if they were. I'm pretty sure that they are corpses animated by spirits (Much like the coffin guy). The difference between Mummies and Dracula is that Mummies exist in the real world. The one in the mansion (in my assumption) is a ghost of a mummy, since he has the glowing green/blue look.