Has your aunt had the dog at a park before? Out of curiosity, what organization is the dog from? (I ask because we puppy raise for Leader Dogs for the Blind.)
I have not had our puppies at Disney, but they have been to Worlds of Fun, Silver Dollar City, and Six Flags. When I worked in Fantasyland, service dogs could ride any of those rides that were not suspended. Anything in the air or anything really dynamic will be a no go. Honestly, Disney is the most accommodating park I have seen.
I'm sure your aunt has this down to a science, but here are some tips just in case. Remember, I deal with puppies who are still learning, so my experiences may not 100% match yours, but will probably be similar.
1. Don't expect the little kids to know not to pet. Adults will try too so you need to be watchful and proactive. I have more issues at theme parks than I do elsewhere, probably because of the sheer concnetration of people. Normally a polite, "I'm sorry, she's working" does the trick.
2. Be prepared for the weather. If it is hot, he may need booties. We always have a collapsible water bowl and water bottle with us. IF it's hot, we take extra breaks and find indoor things like shows and restaurants at midday if the dog is tired.
3. Price the kennel in advance and if you are doing commando touring, consider doing a dog free day in the middle to give him a break.
4. Scope out the relief areas in advance so you know where they are.
5. Get the info on rider swap ahead of time so you can plan it out. You can also download the guidebook for guests with disabilities which will let you know which rides they can go on and which require a swap. Rider swap is very easy to do. One person stays on the mdiway with the dog while the others ride. They let the CM know they are doing a swap and they will get it set up for you. Whoever waited with the dog then goes back up with one other person (so someone gets to ride twice.) It is super easy. If you are using Fast Passes, the person who waited will also need to have a fast pass.
It can sometimes be a little stressful having a dog in the parks, but with a little prep, it can be a lot of fun. We love getting pictures with the characters and most characters love the dogs! Pluto and Snoopy are alays cute ones to do. Good luck!