http://travel.state.gov/dominican_republic.html
"In an effort to prevent international child abduction, the Dominican Republic requires that minors under 13 years of age traveling alone or with anyone other than a parent must present written authorization from a parent or legal guardian. This authorization must be notarized at a Dominican consulate in the United States."
I don't know for sure, and if it is anything like bringing a container into the country, you will never get the same answer twice no matter how many embassies/consulates you call!
Best of luck. I would err on the safe side if at all possible.
marc