So far as I've heard there have yet to be any rulings on what may be considered exploits in BF3 but personally I'd let it ride on any of the maps where there are air vehicles already. Getting to high places from a heli or jet is pretty easy but it's almost a waste of a player since real long range sniping is so much harder than it was in BC2. Also, you're easily spotted and quite vulnerable to opposition air vehicles in those places. As for Tehran, Metro, Bazaar and Seine, definitely an exploit.
Edit - The two spots they show on Caspian can easily be reached just by dropping a spawn beacon in the right spot making the MAV more trouble than it's worth.