For Seaworld, and other Anheiser Busch parks, they recently changed their discount. It was free admission for up to 6 people with a valid ID. Now it's 50% off. The link is as follows for this.
Military Discounts on Theme Park Tickets | Waves of Honor
For Disney the website is as follows:
He can purchase through ITT, at my reserve base it was $5 cheaper through our ITT then purchasing them actually at Disney. You can get 6 passes, however one pass has to be used by the sponsor. This is for friends or family. We have used it a few years in a row now and it's really a good program. The sponsor has to be there to activate the cards but, after they are activated, they can be used by the person who is given the cards anytime.
The military camping is great too, sometimes hard to get in at some locations but, well worth it. We goto one near the beach in Delaware near us and for the price you can't beat it. We plan on visiting more so it's certainly something you'll want to check out.
Good luck! Tell your Son, thanks for his service!