It is impossible for Zarek to be a CYlon because he's been a public figure for something like 30 years.
Yet, cylons are popping up in four thousand year old temples. I think we're in for a complete redefining of what exactly a cylon is. And, I don't think it's going to be "they rebelled, they evolved, there are many copies, and they have a plan". At least, not in the sense we've been lead to believe. They don't know who programmed them or where they came from. Something is up.