Yes, they say maximum of 9 divers per boat. We were there at the end of September last year and we never had more than 4 divers in three days of diving. I know they have more than one divemaster on staff, but not sure of the policy on quantities of divers per divemaster. They are great to work with and are very responsive to e-mails, so I'm sure they'd be glad to answer any questions you might have.
I have a relationship with the owners of the dive shop at Las Rocas. They have another operation at Media Luna Resort on the east end of the island and I book trips for them. I know them to be good people who run a safe operation. Their divemasters were really good at leading dives, spotting interesting things to look at and assisting divers. We only stayed with them once and did three days of diving. Sorry, but we did not rent any gear so I can't comment on that.
The thing we liked so much about Las Rocas is the location. It's at "the end" of West Bay beach. While the beach, restaurants and bars are nearby and easily accessible, you're not right in the middle of them so there is no thru traffic in front of the resort. Peaceful...beautiful...friendly.