@literally45-- I use diluted tea tree oil sometimes on my dog. But I dilute it a lot, use very little and I put it on a part of his body that he can't lick off. I think when used in very small amounts and when it's diluted, tea tree oil won't harm a dog.
That being said, some dogs can be allergic to tea tree oil just as humans can be. So one dog might be completely fine and another might get very sick.
It's a good idea to consult with a doctor about this. If tea tree oil is used in any form, you must keep a close eye on the dog for a while for any adverse reactions. If you do do see any symptoms, the dog should be rushed to a vet immediately.