Well, I have bailed out and stood on the runway and shot aircraft trying to take off.  .45 rounds to the canopy does the trick.  While there I could see the manned ack up, but no one was shooting at me.  If only I could take control of the ack.
Yes, people would have to be blind, or at least not paying attention to what is happening.  It is hard to see a troop on the ground while flying around or driving a GV. 
Just an option that I thought might be fun, especially at a vehicle base where the manned ack could do a good job on the hagars.
As to taking control of a gun, it seems realistic to you that you can jump from a fighter, to an attack plane, to a bomber, than to a tank, a jeep, and the manned ack, all in a few minutes.  It is a game, just trying to get some fun options for a downed pilot.