From posts on this board the only zipline on the mainland from SP is Tanisha Tours, my guess it's the same as where you go thru Jaguar Paw. As for tour operators, we will try to use Tulu an indepedent who will custom our trip. But there are many, best bet talk to the hotel and they can probably hook you up.
The snorkeling around the reef is excellent, most areas are pretty shallow so diving is not really a requirement. To places outside of the reef like Blue Hole, I would think you would need to be certified, but not sure, not a diver.