dammaged event handlers are related to the "hit points" LOD and class hit inside the config, but even though if you do everything OK still ArmA won't recognize them, somehow ArmA has bind dammag and the appropriate EH with the simulation type, so if you have a TANK dammage EH will be triggered by the appropriate class names, of the class Tank and its children.
You can trick though somehow the engine by assigning a different class name for something else, as an example i take our huey, in which we have put the Hit class for missiles, but instead for missiles (since huey's don't have missiles) we put the flap in it, everything works fine then.
So we are alwasy limited by the hit class of the specific type of vehicle (i hope/wish) in ArmA 2 they will expand them a bit more.