I also have a service dog, guide dog at the moment and my first dog who I still have is now retired but was a service dog for my seizure.
First let me state, that I to would find it very hard to believe this dog is a service dog. Originally it stated that the service dog had to do 3 tasks for the individual. I am not an expert but having a dog carrying a oxygen tank does not seem that s/he would have enough training to handle all the distractions you will come across in WDW.
I have had both my dogs go to Disney. My both did okay, but training was a key key issue. My first service dog was a challenge, needed a lot of breaks and a lot of rest and quiet time, so I will say he spent a lot of time at the kennel and we choose not to bring him next time.
My guide dog went, I have been legally blind since 4 but because of seizures that needed have under control before I could benefit from a guide dog. Anyway, he was trained at a school, bred just to be a guide dog, with a school with over 60 years of experience just raising dogs to be guide dogs. Even he was a little distracted.
The ground is hot. They are walking and standing more than 5 miles a day. They are doing it more than a few days. You will need to carry a bowl for water, especially if the dog is carrying extra weight. You can either have wax put onto there paws or use booties. (antoher reason I question that this dog is a truly trained dog, because both of my dogs, that were trained were trained with boots on. If this dog is not a probably trained dog and just a dog you are taking and going to pretend that the dog is a service dog, you must also know what you can not do with a dog, you can not take them on escalators or moving side walks, there have been horror stories about this, where dogs lose paws, unless of course the dog is wearing booties, which you have already said the dog has not been trained to. I question who trained this dog, for that alone, dogs paws get stuck and can cause serious injury to the dog and if a dog has proper training of $20,000 for a mobility trained dog, or $40,000 for a guide dog, what trainer would not train with booties on, knowing the dog at some point would need them on. So Haunted Mansion and other rides are out.
Also, be away, you can not leave a dog unattended in Disney hotels for more than a few minutes, like to run for a soda or get laundry. Also, be aware that an untrained dog should never be put on a plane, you never know what could happen when up in the air with an untrained dog.
Also be away, that every person mostly adults will stop and ask to pet, or try to feed the dog, or stop to talk about the dog. These are all a lot of distractions for a dog, never mind a person who is walking the dog in a very crowded park.
Also, since it seems like a lot of people question the dog may not be a trained dog covered under ADA, it is not a giving that it will be allowed, Disney may ask you to remove the dog for behaviors, for barking, for not being housebroken. Under ADA they have the right, so be prepared with everything you need to put the dog in the kennel or to go home if need be.
A dog in a resteraunt who starts sniffing for food, and eating it off the floor is not housebroken and can be asked to remove the pet from the resteraunt or the park.
I was at the park one day when this happened. A service dog, with vest and everything was barking, he grabbed an ice cream cone from a little boy who was in a stroller, when the mother yelled and jumped the dog growled, and there was other signs I guess, the dog was asked to leave. The dogs owner was saying that it was a service dog and was allowed. But by law disney had the right to remove the dog. How I know to question the owners truthfulness about the dog. She offered his papers, which by ADA law has any barring, Disney can not ask for them and most true owners of service animals would know not to offer. She offered a letter from her doctor, again ADA laws clearly state that Disney can even except, just like with a GAC card that is why it is not necessary to bring a doctors order.
I can not say for sure that this is not a trully trained service dog. But I know many pet owners who say the dog is a trained service dog, yet the dog has a history of biting. Which most owners will not let you know. I know many persons who use emotional support dogs as service dogs but these dogs have not had the training. I know sereral persons who had small lap dogs that say there dog is a service animal, when asked what there disability is they say a back problem, when ask what task the dog does, they say support them, come on a 5 pound dog supports the weight of a 160 women. I don't think so.
The school I went to have dogs for children who are blind and for autism. They tell the parents right up front although these dogs have been specifically trained for the child's disability, and help admensely they are not service dogs. These dogs by ADA rules do not fit into the same catagory as service animals, since they can not be control by the child with the disability. The parent is the handler, so these dogs are not allowed to school each day, because the parent does not go to school each day. The parent controls the dog not the child. I can not say for sure, because I am not a lawyer, but ADA I think has a part in it that states that the handler of the service animal has the disability and that the person with the disability must have control of the dog. Not saying these dogs do not give valuable service for the child, and that is why they give them to children who can benefit. Just like I am sure that a cat or dog for elderly, are very valuable, giving them a reason to get up each day and move. But that does not allow them the same rights under ADA.
People can buy service vest on line, they can buy little certificates stating the dog is a service dog. That does not make it right. and I know ADA does not want to limit it because there are disabilities that may be able to train there own dog, but I think a person who would do this would also know the limits as to where to bring the dog. I know that ADA wanted to word that only large breed dogs were service dogs, but they cut it off and did not pass this section. Allowing some with say seizure to have smaller breed dogs.
So in closing, if your dog is a true service animal, I hope he has had the training to go to a place like disney, adverse effects could turn a good service dog into a retired service dog, because of the stress they are under while there.
If not, or to all those who want to pass off a pet, please think of the stress you put the dog under, the risk you put others under and question if that risk is worth it to all involved.