We used to have a dog with "issues." We typically boarded her with our vet as they were fully aware of her issues and her file and kennel markers were very clearly labeled for all of the techs. She was prone to dog on dog aggression as well as fear biting...but the vet was great with her. It was also the only way we could go away as I didn't trust having her around anyone or hiring a pet sitter.
Our current dog is far less of an issue, but I still stick with the one place we've come to trust. While she is jus wary of strangers and more aloof with unfamiliar people, she's also very high energy and after some of her more costly "antics" in our home- I could never bring her on vacay and trust her in a hotel room. I also know she gets more attention while we're on vacay by being in the boarding facility. i.e. they play with her several times a day, let her run, etc. which sounds far better than being cooped up in a room.
Ultimately, I think there are too many careless people and too many secondary issues with allergies, fleas, etc. for it to ever be permitted at WDW.