female cat in heat with neutered male

Among my many cats I have Skyler, 1.5 years, all white, who is going to a new home next week. She is currently in heat and my 2 or 3 year old neutered male Willoughby is noticing. He mounted and bit her neck a couple times. Since he was loose and unneutered when I found him about 3 months ago, there are probably many mini Willoughby's out there. He is obviouly experienced. Is there really any harm in him displaying this behavior around her? That is all he does and then he usually falls over and tries to play with her. He is literally triple her size. If he does know how to mate with her, nothing will happen since he has been neutered for 2.5 months now. Any harm here or should I seperate her?

A neutered male can still copulate, but is essentially, "shooting blanks" so no kittens will be conceived. But since it is the act of mating itself which causes the female to ovulate, this behavior, if allowed to continue, can result in a false pregnancy. While this doesn't normally present a real health risk, I would probably go ahead and separate them.