Is a moisture barrier needed over gyp-crete (gypsum concrete) for wood / bamboo flooring?
The answer is :


It depends


Above grade doesn't mean above ground, necessarily.  

If you are referring to concrete that rises out of the ground - then yes, you should put down a moisture barrier.  Concrete is porous and moisture will (slowly) permeate the concrete if there's enough moisture around.

However, if the concrete is suspended - a concrete floor above ground with air below it - then no you won't need a moisture barrier.