I think that Lampkin is Baltar’s brother or in some way connected to his past. My main reason for this is the fact that in the “Dirty Hands” episode when Baltar was talking about his secret past as a farmer’s son on Arelon, he started speaking with a different accent, and even a different voice. I thought that it sounded like a pack-a-day Liverpool accent, and Lampkin’s voice and accent was almost identical. Anyway I doubt that I am the first one to bring this up, but there it is.
Several people have written in on this one, including Angela Earle and anonymous others. The general concensus seems to be that there’s some significance to Lampkin’s accent, although what that might be varies with the responses. Personally, I just figured that’s the actor’s accent, since he sounded just like that as Badger on Firefly. But you never know… sometimes the smallest detail can be important in BSG.