River13 is correct on both counts. You go by Regional Boards and State license just like everyone else.
Also, some endo programs have a strict requirement of some type of experience after dental school such as so many years of private practice, a GPR, or Military experience. The reasoning for this in my mind is that you will be asked every day to pass judgement on teeth that are sent to your office as to whether they are restorable or not. If you don't have experience in doing these difficult restorations yourself, it's hard to make a credible decision. You also have to able to judge the abilities of your refering dentists. Several years experience beyond dental school in the real world of some type is thought to help you in this.
If you are a very outstanding student, these programs have a definite interest in you for various reasons. I was the first applicant to be accepted at UCONN's endo program right out of dental school. See some other threads (many) discussing how to stand out among others when applying to endo programs.
Good luck out there. I've been an endodontist for about 20 years. It's good but difficult.