Although I am far from an expert on the matter, I believe the ACGME requirements govern residency programs and are terms for them to maintain accredidation. To be eligible to sit for boards, you must meet the ABOS requirements, one of which is to graduate from an ACGME accredited program. You will probably want to check with the ABOS to see if there are any specific requirements for the intern year to be able to sit for written boards. If there aren't, then you will likely not need to give up any vacation time for additional rotations. Simply graduating from an accredited program will likely be enough.