I assume you can document that the trip is legit and that he plans to return? Most of the time, if your have a scheduled pleasure trip, you should be able to receive a PO's permission to leave the country while on probation. But do not delay in asking about this. If the PO denies the request, you can take the matter before a judge and ask the court for permission to go on the trip.
He certainly can leave the country while on probation for DUI if the PO gives permission; however, an alternative is to ask your attorney to file a motion for early termination of probation. This assumes he is not under a state mandatory probationary period.
If he is on a state mandated probationary period, it may be beneficial to have an advocate (such as your attorney) asks the PO for permission on your behalf. If permission is granted, don't be surprised if he is drug tested by the court upon his return.
If your boyfriend is on Probation in Montgomery County, He should go to the Montgomery County Adult Probation and Parole office and speak with his probation officer ASAP. The Probation officer can grant him permission to leave the country while on probation. However, in most cases the Probation Officer will want to see that person has been compliant with all terms of probation. In addition they usually will not permit leaving the country for vacation while on probation if all of the persons fines and costs have not been fully paid. Your boyfriend would have a better chance of getting permission to travel if he first goes to the Clerk of Courts and pays all remaining fines and costs including any remaining state monthly supervision fee for the remaining two months.
A Word of Caution!!! I have had clients who have traveled to the islands with permission of thier PO and when they got back they were drug tested and then violated and got no credit for the time they were already on probation. So let your Boyfriend know that what happens in Jamaica does not necessarily stay in Jamaica.