January 2006 I did the Whale watching tour while staying at a resort in the Dominican Republic.
From what I observed, there was no snorkeling or diving allowed in the area. First of all the whales move at a really fast pace, so it would be impossible to dive with them. Secondly it was only an educated Captains guess to where the whatles might be. (Versus going to Stingray City -- where the rays have been fed for so many years they find you.)
I was really pleased how the DR regulated the Whale watching "procedure" each boat could only stay a specific time by the whale/whales, then they had to move out to let another boat get closer to the whale/whales.
Then the Captain proceded to locate another whale. I thought the whales traveled in large schools like fish and they do not. Was really thrilled to see a mother and child.
The hotel I was staying at didn't offer Whale watching in the "tour" brochure, that should of told me it was really too far to travel to. But I asked and they located a tour for me. I left at 6:30 a.m. and didn't get back until 7:30 p.m. that night. Despite hours of being on the bus by myself before we picked up the first group of hotel guest, I was thrilled I did the tour.