My DD9 has moderate bilateral loss AND has grown up going to WDW. She is now old enough to use the closed captioning, etc. When she was really young we found she enjoyed most of disney, but it was visual, not auditory.
One problem we found was LOUD noises. She doesn't hear the "warm up" noises, so to speak, so the loud noises sneak up and startle her. Rides like Universe of Energy, Honey I Shrunk the Audience, etc., scared her because of the sudden loud noises. Fireworks also really did her in.....pretty lights but lots of sudden booms. Our solution was to take OFF her hearing aids and have her wear earplugs. We also tried to explain what was going to happen, and give her the story line BEFORE we went, so she new what to expect (for example, at Fantasmic the bad guys just arrive- she doesn't get the story line so she doesn't understand why they suddenly appear).
We use a small business card and write on it "please speak up and look directly at _________. She has hearing loss". When we met a face character or CM I would just show them the card quickly to let them know about my DD. Really, really helped- the CMs typically get down to her level, talk directly to her, and often give her just a little more TLC! Made and makes all the difference in the world. Using a small card prevents embarrassment for kid and gently tips off the CM without making you look like an overbearing parent! Costumed characters are no problem- they don't talk anyway!
We did get a GAC and use it to sit close at shows so our DD can better see faces and facial expressions. We NEVER used it to avoid waiting (and I don't think the stamp would allow you to do so), but it helped us get seating that made it easier for her to enjoy the show. Most rides don't need any special accommodations.
One more thing- be sure and let lifeguards at the pool know about the hearing loss. If the lifeguard hollers at the HOH kid, the kid may not respond appropriately and may "get in trouble".....letting the lifeguard know helps both the lifeguard keep an extra eye on your child, and avoids the embarrassment of getting hollered at when you can't hear!
That's all I can think of immediately, will add more if I can think of anything. Talking Hands is the resident expert- her help has saved me more than once!
Maybe we send out a call to Talking Hands! Where are you!?!?!?