Character Analysis
When Nina first runs into Dermid, he looks pretty shady: "he was large and sunburned, with a vicious scar on his cheek. His oily blond hair had been combed straight back" (10. 28). He also—creepily enough—winks and leers at Nina when letting her, Dave, and Father Ramon into the match, saying, "Enjoy yourself, love" (10.54). Ew.
Dermid isn't the brightest crayon in the box, either. When he and his dad get Reuben back, Reuben pretends to be asleep, so Dermid only partly ties him up. This means Reuben can get free and tackle Dermid before Dermid can do much damage during the rescue attack. In fact, the most Dermid does is curse a bunch: "Ahhh! Ahhh! You bastard!" (22.62) Not exactly who we'd want on our side in a fight, that's for sure.
What does Dermid do once Horace fangs him? Mostly he throws up. When he manages to escape, he bites his own dad (yuck) and then goes to take Nefley hostage. In his defense, he's not thinking clearly, which we see because he comes right back for his dad, unaware of the whole vampire bite thing. That vampire infection is serious business, it seems.
Vampire life doesn't really suit Dermid; he's constantly weak and sick after his transformation. But at least he won't be profiting off werewolf death matches anymore. And given how he did for so long, you might even say he gets his just desserts.