Most of the schools that you would like to work in as a secondary teacher in the DR do require certification for most of their teachers since they are accredited by agencies like SACS and to keep accreditation need certified teachers.
Unfortunately you have missed the job fairs that many schools attend to hire their foreign-hire teachers. But if they weren't able to find a good match then perhaps you might luck out and fill a vacancy that way.
Get certified and then you can teach in private schools almost anywhere in the world and get the experiences of a lifetime to go along with your paycheck.
From personal experience I recommend that you use the hiring fairs from International School Services or the fair at UNI.
International Schools Services
Fair Registration Process
Good luck in your search.