The way I heard it, he got a lot of input for Dune from John W. Campbell, and none for the sequels, which may explain why the sequels suck by comparison... and I stand by my comparison to Lawrence of Arabia.
It's fiction, John. Herbert made it up, using history as a guide for some of it. Paul was obviously inspired by Lawrence. The Fremen are Bedouins. Stilgar is Auda Abu Tayi. No channeling of the past needed. Just a basic knowledge of WWI in the Middle East, and a good imagination.