Upvote:9
The term "adjacent islands" is defined for the purpose of immigration law at 8 USC 1101(b)(5):
The term βadjacent islandsβ includes Saint Pierre, Miquelon, Cuba, the Dominican Republic, Haiti, Bermuda, the Bahamas, Barbados, Jamaica, the Windward and Leeward Islands, Trinidad, Martinique, and other British, French, and Netherlands territory or possessions in or bordering on the Caribbean Sea.
Source: https://www.law.cornell.edu/uscode/text/8/1101
Traveling to the Dominican Republic therefore will not reset your VWP clock.