In all my years, I have never seen a neutered male harm a kitten ... I've seen them act like Momma, I've seen them play and frolic with the babies, I've even seen them try to nurse them - but I have never, ever seen one intentionally hurt. However, I do agree that it is best to err on the side of caution and keep the male away from the kittens at least until they are older.
Usually, a neutered male, especially a young one, will just play, chase and romp with the babies. Yes, the play needs to be closely monitored due to the sheer size and strenth differences, but normally, they play together well. It actually helps the kittens to learn social behavior.