Here is some things to consider when it comes to vulching in FSO.
AC that are on the ground re-arming, in most cases, do not have to sit there and be shot by incoming enemy. There is no reason that they can not tower out and get a successful landing long before an enemy AC has the chance to fire his (or her) guns.
Vulching as it occurs in the MA does not happen in FSO. In FSO you do not have a situation where enemy AC are circling a base shooting AC as they try to spawn and take off. The only vulching you are going to see in FSO is enemy AC that find AC on the ground refueling, or on final approach, and they shoot them on the ground. But then again those AC on the ground should have plenty of time to simply type .ef and go to the tower, giving the enemy nothing to shoot at.
In the case where that AC is still moving after touching down, and can not use the .ef command yet, said AC should be being covered by friendly AC still flying. And very rare should be the case when a pilot is trying to land with enemy AC flying close enough that they can get a shot on him before he can type .ef.
So, FSO is about scoring kills on the enemy. If that enemy is going to give you the opportunity to kill his AC on the ground, then take it. I would, and most pilots in WWII would as well.