Hi Skip,
I was in your son's shoes last year. Nuke was my 5th of 5 choices and I was selected as a Nuke Power officer during service selection (NROTC) in October of 2014. I managed to get redesignated as a pilot and I'm in Pensacola now, so it can be done, but managing expectations is the key here. The bottom line is it's unlikely.
The advice I would pass on to your son: he was selected as a Nuke Power officer and needs to begin preparing for that. I understand that is easier said than done (being selected for naval aviation was my dream too, and it was devastating to have that taken away from me), but sometimes that's how things shake out in the military. He needs to work his ass off preparing for the nuke technical interviews and the interview with the Admiral. Being bitter and trying to throw the interview to get redesignated is not going to get him very far, so tell him to work with his nuke adviser and do the best he can on the interview. In my case, they seemed genuinely impressed with how well I was prepared for something I didn't really want to do and that was HUGE when I went to the redesignation board.
That being said, he needs to make it clear that Nuke was not his first choice when he is interviewing. I went with the "Nuclear Power was not my first choice but it was an honor to be selected for such a prestigious and challenging career," line. I also assured them that I would give 100% in the training pipeline and in the fleet despite it not being my first choice. All of that was true, I wasn't trying to blow smoke up their asses. Neither was I trying to tell them to go screw themselves. At the end of the day, it's a career a lot of people would kill for with (arguably) the best opportunities after the Navy.
If he makes it clear to the Admiral that he wanted to be a pilot at least he can go the rest of his career knowing that he didn't roll over without saying his piece. Also easier said than done, trust me. Telling the O-10 that you don't want to be a part of his kingdom is not a fun conversation, but if you do it with tact, professionalism, and honesty it goes a lot better. More people than you think get nuke drafted. Sometimes you are your best (and only) advocate, and this is a time for your son to stand up for himself. I'm sure people will disagree with that and you'll likely get some "grow where you're planted" arguments, but the bottom line is I knew 2 other guys who interviewed with me who were nuke drafted but wanted pilot as their #1. Both of them are at nuke power school now and I'm in flight school. What's the worst that can happen by being honest?
If your son does not get selected for Nuke at his interview, he is by no means a shoo in to get redesignated as a pilot. I was extremely fortunate that everything worked out as it did for me. I was prepared to more than likely be redesed as a SWO. That's what has happened in the other cases like this I've seen, so your son needs to do some soul searching to see if he would rather not just stay a nuke (and make $$$).
Bottom line is it is extremely unlikely he will be able to redesignate Pilot or NFO (from what I have seen). I am extremely lucky that I am in Pensacola, not Charleston, today. My best advice for your son is to tell the truth, do his best, and let the cards fall as they may. Some things are just outside his control now. But he shouldn't take it laying down. The person who cares the most about his career...is him.
Feel free to send me a private message, I'd be happy to provide more details or get in contact with him if he wants.
Best wishes