I think it is safe to say that the Christian is not Jacob. And, his presence in the cabin does not prove that Jack’s dad is alive. So, was it Jacob that approached Hurley in the window? Here are three screen caps. The first one is what we think is Jacob’s eye from “The Beginning of the End.”. The second one is Jacob’s eye from “Man Behind the Curtain.” The last one is a reflection of Jack from the end of “Through the Looking Glass.”
Doc: I’m nearly convinced that the secondary character – whose appearance jumped me out of my fricken skin – was in fact Desmond. How could it be Desmond? Simple, when he went all failsafe on us, he was somehow cast into multiple timelines and one of his copies went into the ether where all the dead people go. Something similar may have happened to Jacob.