The requirement of owning the vehicle for one year or more only applies if you are applying for an exoneration of the vehicle. If you do apply for and receive an exoneration, you can not sell the vehicle for five years, not one year.
Fabio Guzman is correct. Unless you are completely familiar with the Dominican customs departments and the port where the vehicle will enter the country--and the officials in that port, you are better off buying a vehicle here. In this case, a customs broker will only submit the papers. They will not fight the excessive, and often incorrect valuations, etc.. For example, last year, I moved back to the Dominicna Republic from Guatemala and brought my furniture and five year old (1976) van back with me. Customs initially valued the vehicle as a 2001 model and I was told that the taxes were more than the value of the vehicle in the U.S. The problem was resolved but it required multiple trips to Santo Domingo from Santiago.