By how many degrees is it off? Is it off by the same amount of degrees every time?
Regarding the Reaper, yes it (and the ground units, if ordered to mark targets) at all times if the target is in range/in sight and switch when the target is destroyed.
Yes, vehicles only does exactly that. I had an instance where I had my gun dry but a sixpack of GBUs, in that case a MANPADS is a very low prio target.
Remember to first turn laser off and then on again if you want to use this feature.