I've been on a couple of Windjammer trips. They aren't really geared to scuba divers, although you can make arrangements to dive with an outside dive op. I did this successfully in St. Vincent, really enjoyed the dives, but on the next day not enough divers signed up to do the dive trip so I couldn't go. Bummer.
Windjammer is a no-frills, laid-back way to see the Carribean. I didn't look at your profile, but if you're a young person looking for partying, this probably isn't the trip for you. If you're an older, parrott-head type, you'll love it.