*disclaimer* I have never installed arma.
each vehicle in the server has a specific ID? when you spawn a vehicle do you set an ID for it or is it dynamically generated? if you are placing an ID, what would happen if you set two vehicles to the same #?
Each vehicle has an ID, this ID is relative to the type of vehicle we're working with.
For example, what's named a "Bus" ingame, has the actual vehicle name "Ikarus" in the class list
The best example is using a humvee, it can have different attachments such as the .50 cal, the M2 CROWS sheltered machine gun, and grenade launchers.
Each of these humvees has a slightly different identifier, that's not unique.
Check this out
http://community.bistudio.com/wiki/ArmA_2_OA:_Vehicles