In the show Caprica, they use several actors who also appeared in Battlestar Galactica. Caprica is supposed to have taken place at the very beginning of Cylon creation (well before the advent of human-form Cylons). Are they trying to tell us something we didn't know, such as Cylons outside of the '12' or were the creators simply using actors they knew and liked? If the latter is true, it seems a bit tortuous and demonstrates a blatant disregard for fans. They, surely, must have known that endless theories would be presented in an attempt to explain this.
Ronald D. Moore spoke about the re-using of actors from BSG in Caprica. Although he doesn't specifically reference human-form cylons, the clear implication is that casting decisions are an out-of-universe decision and that fans shouldn't read any special significance into it.
Is the re-using of actors from Battlestar in Caprica, is it a direct reference to ancestry?
We're kind of being vague about that. We're not really specifically saying that those are the actual ancestors of the characters they played, but if the audience would like to think that, there's really no reason why they can't.