Okay, he's the deal: I think what will likely happen is that Fright Train will be one of Bunker's nemeses. He could have another, but Fright Train will just be one of them. I think the point of Vengeance is that the Vengeful Five are all nemeses of Freedom Five members (or at least consider themselves to be). So while they might not be THE nemesis for each hero, I feel like the nemesis icons will come into play.
Considering the two reveals so far (Fright and Ermine), I get the feeling that all of the V5 are the Freedom Five's nemeses in a "Dude you are not my nemesis" way. The Freedom Five members don't even give them (individually) a second thought, but when they start working together they become a serious threat.