I didn't know about the book, but I'm finding nothing at all to indicate that he's ever lead employees in singing hymns. At Intel his boss was a secular Jewish man, and so was his CFO. That leads me to doubt that it ever happened especially not at Intel.

Based on my brief interactions with him, and my overall experience with Intel as a project partner at the time, I'd say he has exceptionally high integrity. I'd bet he didn't even have his books ghost written.