Basically, Wolfen just sounds like straight-up SF. I haven't read it, though, so there might be supernatural elements as well.

"The Hunger" by the same author also had a species that were the basis for a supernatural creature- Vampires. That made the book mostly SF, although the main character's current companion did have some possibly supernatural experiences. He experienced something like the ghosts of the people he killed at one point, although that may have just been a hallucination.