Fallout Wiki, on how James got in: He was able to enter the Vault because they needed a doctor, this is shown during the "One Year Later" scene. The Overseer states "We need a doctor, not a deadbeat- fail to meet my expectations and you'll be out on your ass. James and his cheery charities are over." This is what I thought. People just didn't come and go, they just let him in because they needed him. But letting even a single person in to a formerly sealed vault is still pretty big and controversial, especially since the vault's mission was prolonged isolation study..