Sorry, but there's no one here that.can last the chances. Just like when people post their resume and ask what are my chances for receiving an appointment. You simply apply, go through the process, and see where you end up.
For most of the medical concerns having ever been asked, e.g. asthma, etc... Some receive a waiver and some don't. If they consider your son competitive, they'll consider a waiver. But we don't know if he is competitive because we dont know who is competition is. We've seen 4.0gpa not receive an appointment and we've seen 3.6gpa who do receive an appointment.
It's real simple. You apply. If they need more info, waivers, etc... They'll tell you. You'll either make it or not. You can try and determine if its worth your time applying. You apply, along with a minimum of 4 other traditional universities. See how many say yes, then accept the one you want. Sorry i cant give you a reassuring answer, but no one can. Best of luck.