My Insipre 1 Raw gimbal does not have a slot for the copter's key to go into. (See image.) Therefore, the gimbal is attached only by the gimbal lock on the copter. It certainly appears precarious and unstable.
I haven't had this problem, but I would urge you NOT to fly it this way.
You have far too much $$ in that camera to lose it.
That key carries half of the load.