Now there's a correlation I hadn't thought to examine.
Look at what Romans 11:25 is actually saying will happen: as long as there are Jews around, they will not see the divinity of Jesus and will argue against it. Well of course this was going to happen. In practical terms, Jesus didn't do what they expected the Messiah to (standing up to the Romans would have been a good start), and it was the Jews whose representatives supposedly got the guy killed. To acknowledge Jesus as Lord is downright un-Jewish.
I refer you again to my piece on prophecies, and suggest #1. High Probability of Success as a far more likely explanation for the accuracy of this prediction. In other words, it was a no-brainer.
Meanwhile, the cultural background of these atheists is irrelevant to the soundness of their arguments and counter-arguments. If you want to call them Jewish atheists, go ahead, but it doesn't invalidate a thing they've said or written.
One atheist writer who certainly doesn't fit the supposed pattern is Ayaan Hirsi Ali, a Somalian ex-Muslim. Possible other exceptions are Dan Barker, Richard Dawkins and Brian Sapient as you say, plus Daniel Dennett, James Randi, Michael Shermer and Victor Stenger. I haven't got a single Jewish ancestor as far as I know.
I find your defenition of a Jew interesting. It's in line with that of the many religious Jews who essentially declare Judaism hereditary. By this logic not only is it impossible to stop being a Jew (from your list, only Hitchens self-identifies as a secular Jew), but one is born a Jew. Thus you needed to call yourself a gentile as well as a Christian, to emphasise your lack of Jewish ancestry.
Importantly, for the prophecy to even be accurate, the above definition must be the case. Do religious Jews (or does anyone else) have the right to label those who would otherwise be known as ex-Jews?
For those who came in late: Zeitgeist puts forward three major theories, the first of which is that the character and story of Jesus is based very closely on the Egyptian god Horus, and thus Christianity is descended from sun worship.
I would first recommend contributions to this site by Rook Hawkins, and those on the main RRS site (link at right). Next, just google "Zeitgeist Horus" and you'll be swamped with counterpoints. It's as if there are as many Christian responses to Zeitgeist as there are Christians who've seen it.
All up I'm terribly skeptical of the specific claims about Jesus in Zeitgeist, mainly because the other two major claims are way into conspiracy theory territory. So I wouldn't use it to examine doubts like yours.
Pick individual aspects of Jesus' life and research them out of context: virgin birth, exile, healing by touch, resurrections, posthumous appearances, etc. You'll find tons of examples, many of which pre-date 1 BC by centuries. If Jesus' story is based on something earlier, it doesn't have to be Horus. It could have come from anywhere.
If you like, come back and let us know what interesting stuff you find. Best of luck.