Dogs and pets are allowed in some parts and areas of the Yellowstone National Park.
But dogs and pets are not allowed in any hotels that are within Yellowstone National Park however some cabins in the Yellowstone National Park do allow dogs and other pets.
There should be posted signs in areas where pets are not allowed or dogs are not allowed stating they are prohibited in those areas.
But in most of the other areas the dog can go into Yellowstone National Park as long as it's on a leash at all times and is not aggressive.
If the dog is not on a leash or becomes aggressive the dog will be told to leave along with you.
So as long as the dog is not aggressive or doesn't bark constantly and is on a leash at all times when outside the cabin then the dog will usually be allowed in those areas.