I've noticed some differences in the cabs on the LVS vs. the HEMTT are the skidplate openings, the lack of a right rear window, the vent arrangement on the roof is different, there is no clearance light on the corner of the cab on a LVS, and most significantly - the intake tunnel that runs up from below the cab to the top of the back of the cab for feeding the huge radiator right behind is a significantly different design. My Hemtt cab has an air inlet on the top of the cab, and the LVS has none.
I think that's about it. They bolt on the same, and they seem to function the same. I can fill you in on more details soon - I am picking up a LVS cab to possibly swap onto my truck in two weeks.