There reason why Moore didn't use the footage is because Moore only used footage of people trashing the U.S. He therefore probably only used 1% of the footage that he shot.
I'm not so sure the reason is that Berg didn't trash the US, my guess is that Moore didn't use the film because Berg was not really a Bush supporter. There is something very strange about who Berg really was, possible connections with Prometheus radio, a George Soros project and just a lot of unanswered questions. Just the fact that Berg's father calls him a Bush supporter doesn't make it so.