My wife, daughter, and I spent a wonderful week at Ocotal Beach Resort in August of 2006. We did local dives, Catalinas Islands and Bat Island with Ocotal Diving. They are a very good operation, but, I must say, the fast boat at Rocket Frog does sound good. In addition to diving, we did several land excursions booked through the resort that were really excellent. We flew into Liberia and had a car, it was great fun exploring and gave us flexibility for restaurants and shopping.
Summer is "green season", a higher chance of rain, which may affect visibility, at least local. We had blue skies and no rain, visibility was moderate and water temp 80-81. I'd like to go back sometime