is it normal for them to never stop and go thru your airplane?
Since you are supposed to be parked when you use them or, if you are not, you are supposed to use taxiways (while GSX vehicles will use vehicle paths
if the airport has them ), normally it shouldn't happen they'll clash into your own airplane.
Of course, if the airport you use doesn't have vehicle paths, GSX vehicles (those that not already on the parking, like the catering or the refuel truck) will be forced to use taxiways and, in that case, they are not aware of other planes.