ahaben,
You made two points. There is no abuse, since this does not mean that they are on official business, in fact service units which are not emergency vehicles also have VAS plates, all it means is that they are a volunteer, if someones has more than one car, he or she can put it on all the cars, this is a regular custom plate you can get one by taking an EMT course and placing it on ALL of your cars.
as I pointed out, VAS plates does not meant that the driver is on official business, so he can use it even when not on call, the fact that he will not get a ticket, does not make this an abuse.
It is his choice if he would like to take the risk and park illegally or not. the plates will not get a ticket dismissed.