I use Seavis in Bayahibe for my water excursions. Though I'm a snorkeler, Martina and Werner are themselves divers and know many great divesites.
mail@seavisbayahibe.com
Mare Nostrum has Italian owners but is in a perfecto location overlooking the bay offering great food. It's not a cheap local eatery though (all beverages are 150 pesos each).
For eateries I'd suggest that you look into La Punta, La Bahia and a favourite of the locals being La Cubana.
Kaki