According to Dolores on this thread
http://www.dr1.com/forums/travel-questions/47699-rob-heres-one-you.html
Dominican Driver's licenses are valid to drive on, in the US. Other posters reported that they've used the DR driver's licenses in various places in Europe as well. I do not know of anywhere that one can obtain an international driver's license in the DR. The DR is however a signatory to whatever international treaty governs international driver's licenses.
I don't know anyone that managed to obtain an international driver's license valid in other countries, in the DR.
Of course I'm not talking about those driver's licenses that you buy, but those that you get legitimately. I have no idea what will happen if you drive in the US on a 'bought' Dominican License. But if you are in an accident, I'm sure the insurance will have something to say - something like you'll have to pay all the costs yourself.