Yes, most speak English because that is their language. This board is an important source of information for people planning to visit the Dominican Republic. Providing the answers to questions are mainly expatriates living in theDR or frequent visitors. Their are other forums for Domincans and there most communications are in Spanish. If Spanish is your primary language, you may wish to check them out.
If it was necessary to be a Spanish speaker to visit the DR, tourism wouldn't be the industry it is. It is the non-Spanish speakers from Canada, Europe and the US that fill the hotels and patronize the shops.