If you are staying at Playa Azul, I doubt that your in-house op will be going very far south and you may miss some good sites. Otherwise, you're going to spend a LOT of time on the water. I never get sick as the port is closed when seas are rough but it's a LONG boat ride south. If I could make a suggestion, you might want to rethink your plans. Rent a car, and drive to the caleta where you will have a wide choice of dive ops leaving and a much shorter boat ride.
Just to quantify, not to disagree - "LONG" is relative. The farthest dive site from Playa Azul is maybe 20 miles, and for nearly the whole boat ride you will be a couple hundred yards from shore. To many folks the sight of land nearby is a pretty good seasickness remedy, and typically the waters are fairly smooth, as the dive sites are nearly all in waters protected from the open Caribbean by the island. In the case of norte conditions when the winds are from the north or northeast, of course, all bets are off.