I'm one who finds it difficult to recommend swimming with dolphins in captivity. It's unfair and not what dolphins were put on this earth to do.
If one insists on doing it in the south or east of the DR, ensure that it's not with Manati Park or Dolphin Island. Do a Google search to see why.
For fishing, this is the one I recommend: http://seavisbayahibe.com/fishing_e.htm
As far as recommendations go, everybody who visits the south coast should do this one! http://seavisbayahibe.com/Saona_e.htm
I've done it almost a half dozen times. You can see a recent outing at: