If you are ineligible for entry into the US due to a criminal record, can you still enter Puerto Rico?

My boyfriend did something stupid in his youth, was charged, and never bothered to get a pardon (it takes a long time and a fair bit of cash to get one). We know he still cannot enter the US (tried and denied), but he has a valid pport (went to the Dominican) and we are wondering if he can get into Puerto Rico, since it is a territory of the US.