Check out createUnit in the command ref, that might help. You can name the unit in the init field.
Looking at your example it seems to me that you have already named your vehicle _jeep1. Try naming it jeep1 instead and then deleteVehicle jeep1 to see what happens ..... _jeep1 might not work because of the local variable thing. (variables starting with _ are local, not global. Would that make a difference here? I have no idea. Suck it and see.)