Tough question. I am familiar with what the North Florida environment can do to most anything made of wood, so you are right to be concerned. Moisture passing through a material that then condenses on a barrier is where there could be a problem. Since the crawlspace is unconditioned, then I would assume that you at least have some means for air exchange or venting and that the ground is covered with a moisture barrier.

Very interesting question. Have you consulted with the flooring manufacturer directly about this?

I would love to hear what you found out... I am not in North Florida (but the Pacific Northwest). We don't have nearly as high humidity, but we do have a lot of moisture at certain times of the year. I am looking to put laminate over an unconditioned, vented crawlspace as well, and wondering about the use of a vapor barrier between the subflooring and the laminate... Hope you post back if you got an answer!