Thank you for rescuing him, you are changing his life, giving him a chance at a life now, so thank you so much for this. You are wise to get him checked out before getting around any other cats. I'm not sure where you live, if you don't have many vets to choose from, but if my vet gave me a hard time, I would probably find another vet. Of course, I love my vet and they are wise to be kind to me since I have three cats and a dog and have been with them for many years, but if they ever gave me a hard time, I don't know that I would go back.
Thank you for taking care of this little guy, and hopefully he will be in his forever home soon.