The fact that you are uncomfortable with it is all that matters and all you need to say. If your friend takes offense, tough cookies for him. It could save his life and if he doesn't understand that, nothing you say or do will change his attitude.
That said, if you can get him some refresher dives first then tag team, one hunter one spotter and switch roles on the second dive, then you're golden. I am hoping to do some bug dives in the near(ish) future with some experienced hunters, but I want to do it as a spotter/hunter pair not both diving as hunters. I'm confident but I'd rather not be so confident that I get careless.
That said, if you can get him some refresher dives first then tag team, one hunter one spotter and switch roles on the second dive, then you're golden. I am hoping to do some bug dives in the near(ish) future with some experienced hunters, but I want to do it as a spotter/hunter pair not both diving as hunters. I'm confident but I'd rather not be so confident that I get careless.