An answer from How can I gauge a vet's experience with reptiles? mentions The Association of Exotic Mammal Veterinarians, which as best I can tell is a membership organization, not a certifying organization. They have some great goals, and I see that one of my favorite rabbit vets is a listed member, but a second, very good, rabbit vet is not. According to Wikipedia, interest in treating exotic pets is the first criteria; additional training and certifications are secondary.
Is there any official certification I should be looking when evaluating a potential exotics vet? If so, what level of competence does it imply?