Meredith
If they can enter the US, then you might want to check the following. I live near Niagara Falls, NY and when I go to DR I fly both out of Toronto and Buffalo. USAIR flies from Buffalo to Phi to Santo Domingo. From Buffalo they could catch either Niagara Air Bus or one of the other shuttles that run between Buffalo and the Toronto airport. The return trip from SDQ to BUF has a tight layover (1.5 hours). I was able to clear INS and Customs and still have time. I sat at the front of the plane so I was one of the first off and was able to walk swiftly to INS and was not far back in the line. Customs went smoothly and I rechecked my bags right outside the customs door.
Jerry