How is he able to manage visits to the vet? There are usually other dogs there when I take my dogs & unless you take him several times in just a few months, the people there are 'strangers' to him.
Many vets either have separate entrances, or will ensure no dogs/people are waiting when the subject dog arrives. My sister has had to deal with dog-aggression from her male GS many times, so things like that are what they do. As for people-aggression (or at least vet-aggression), vets have to deal with this alot. They may simply ask her to put on a muzzle before she even gets there.