Hi Illini_Fan
I was on the Cayman Aggressor from 29th April to 6th May this year and we did make the crossing to Little Cayman. The Captain explained that the issue with Little Cayman is related to the direction in which the wind is blowing and depth of mooring on the reef. I got the impression that the wind could be blowing the wrong way on any particular week all year.
I'd advise you to go for it regardless, the diving on Grand Cayman was as good as Little Cayman and the advantage of the Aggressor was that we were always moored above our morning dive site and were first in the water. And the whole experience was fantastic, great food, great crew, great diving.
The one tip I do have is try to avoid cabin 9 which is next to the engine room and consequently rather noisy, even at anchor.
Darren