Are you going to the border camps, or to the Haitian enclaves elsewhere in the country?
My personal experience is only on the Haitian side of the border, but I would say the same general principles apply anywhere outside the US. I would expect that you can do whatever the DR government says you are allowed to do (and then only within the scope of your practice in the US, obviously). As you wrote, it is probably not going to be anything more than education, unless you're going to have a DR-licensed MD with you to work under. "Rogue" practitioners on mission trips can make for difficult relationships between the foreign NGOs working in a country and that country's Ministry of Health. And the current relations between the Haitians living in the DR and the DR government is quite bad. Do you/will you have any contact with any medical professionals currently in the villages before you head down there? They can surely give you a better sense of the conditions on the ground.
I would be very careful trying to bring in prescription drugs without an import license, if you were thinking about that. And don't bring anything (drugs or medical supplies) that's expired. There is a belief in some Haitian circles that expired drugs are poison (not sure if that's true with the Haitians living in the DR, but it's common in much of Haiti proper).
Although you'll have a translator, you might google "Haitian Creole" before you leave, and see if you can pick up a few phrases, even just bonjou/bonswa (good morning/good evening), mesi (thank you), souple (please), koman ou ye (how are you). Even just saying a few words in their native language can help build trust with people. If you have more time/energy, there's a good book "Haitian Creole for Health Care" on Amazon
Good luck with your mission!