I did the DiveQuest at The Seas last year and had a blast! I didn't actually know anyone in the restaurant, but played with all of them almost continuously. The kids really loved it. All the divers are asked to play as much as possible with the diners and the spectators in the viewing gallery.
You might try calling the restaurant directly and see if they can have a quick under water sign made up on an underwater slate and a china marker and have all the divers wave to your son. I know that the divers would love it, I just don't know if Disney would go for it. It might start something that they really don't want to get into. No harm in trying, though.