Question for experienced dog breeders only?

Yes, if he was good with the puppies last time- there is no reason to assume he will act any differently this time. No, he does not know they are "his" puppies, He is probably just a very nice tempered dog. If your female knows him well and was comfortable with him around the puppies last time, there is no reason to assume she will be any different this time either. The six month old dog is a new proposition- she may be nice or she may be too rough and play way too hard with them even if she is good tempered- no telling- so don't leave her around puppies unsupervised. I used to breed many years ago and some males are nice with puppies, some are not so much. Neutering him probably will not alter this fact. I had a stud who loved puppies- some females were cool with him messing with their puppies- some would chase him off until puppies were older. Not every dog I had at the time was bred to him-I would occasionally send one out to be bred elsewhere- he treated all the puppies alike- he was just a sweet good tempered dog.