Weather patterns have become quite unpredictable so we really don't know what will happen, but March/April are traditionally pretty windy. The problem is in transiting the reef rather than diving once outside, and yes, the wind can prevent diving. In my 5 years of operating a dive center here we've often had the odd 1-3 days with no diving, and if they happened to fall in the middle of your week you'd be pretty upset. On one occasion winds were too high to permit boat transition for a full three weeks (I think that was March), and the island was full of people who wanted to dive. The bars were however very busy - it's an ill wind.......
Conditions now are as calm as can be, but there are so few people here that many businesses are closed and many trips don't happen for lack of a quorum. And of course there's always the possibility that we'll get another Dean - or worse. Maybe the best time to visit is towards the end of high season running into slow, but before "dead". Maybe May/June.
But as I said, weather patterns have become highly unpredictable - make sure you buy good trip insurance just as soon as you commit your holiday money. If being able to dive every day is very important to you, tell this to the insurer and see what a suitable policy would cost you (I suspect it'll be astronomical).
No-one can tell you when you must come nor guarantee what you'll find once you're here, and if they do they're a charlatan, but I hope that's of some help.