On second looks your right, the EMS bag isn't classed as equipment. So sorry, I have no idea how to add it. EDIT: There is a script about getting EMS bags, not sure if adding cars to that will work. I'm no scripter so I couldn't test it for you.
Yes, you need to edit the traits of the vehicle you want to add it to. Just tick the boxes. This is done in the editor: 1. Open the editor. 4. Load the mod. 3. Press F1. (May not be needed) 3 Then select a vehicle and press edit. 4. Then go on traits, and tick the boxes there.
Ok, but that can't be the only reason, they haven't finished that many vehicles yet and it's already long past christmas. If that firefighter hadn't of died it still would have been changed.