Any current you may encounter would be dependent on sea conditions at a given location. The only area I usually encounter anything more that a mild current would be around Rum Point. The swiftest currents usually are present during the winter when the winds help drive them. The current at that location is usually negligible in the Spring, Summer and early Fall.
Coral health will also be dependent on the location you are snorkeling. The healthiest corals are generally found off the East End and North Side districts, certainly not off Seven Mile Beach. Places with great coral are the Rum Point sites, Wonderland, Queen’s Monument and Barefoot Beach.