You need a cedula and then you can apply for the license at the Ministry of Tourism. If you are a foreigner just be aware that they will give you the "run around" and everything else to give you a hard time. "DR for the Dominicans" is the slogan there now.
Hiring a tour guide who doesn't have wheels is like hiring an caddy to give me the yardage and another one to drive the cart.
There are plenty of nice drivers around who can multi-task.