Did the military not teach you anything about chain of command? This person is above you and therefore entitled to manage you, whether present or not. You jumped the chain of command, presumably without trying to address it directly with your immediate supervisor. How do you know, for a fact, that the supervisor was told to back off? Yes, the supervisor should give you some room to spread your wings, but given the high stress/danger environment you are in, they may address concerns that they have. Neither the supervisor nor the facility wants to be left holding the bag if something happens on your shift that could have been prevented.
The supervisor, if hourly, could get the employer in trouble if being allowed to work off the clock, i.e. calling you while off duty to manage things. If there is anything in the employee handbook about working off the clock for hourly employees, the supervisor could get in trouble for that as well but it probably won't help your situation. Is your facility union, if so have you spoken to the union rep about the situation?
The supervisory staff at every job I've ever had were salaried and thus, technically, on the clock all the time. They have also always, at some time, called in with instructions while they are off. I never questioned, nor ever encountered anyone else who has, their authority to do so. This was even when I was a supervisor myself, I still answered to someone. But that is my experience only.

