Yes! I did! I did not experience that initial weight loss honeymoon that may do. That ~5 lb loss that most pp get that first week did not happen to me.
I would be very suspicious if he is actually gaining weight though. Maybe he's eating something that he doesn't realize is not o.k. on the diet? Maybe start packing his lunch so you know exactly what he's eating (and hope that he's not cheating at work)?
It's very difficult mentally to not see results on a diet. I felt that way on Atkins. When all else fails, maybe this diet just isn't the right fit for him?