When I taught I included a small section on finding weapons or dealing with the declaration of a weapon.
Unless the weapon was hindering evaluation and/or treatment it was left in place. If the person is able to act rationally the weapon was left in their control (ask, advise, allow the patient to unload or make safe). If the weapon hindered medical or rescue needs or the patient was not able to control it was to be placed under rescuer's control as personal property of patient and held as such (in empty compartment of gear bag kept just for property of patent that NEVER leaves rescuer's control).
All personal property taken is documented on paperwork. If patient maintains control it is up to them to disclose at each level on their own, however it is to be recorded on paperwork.
As with all things taught each service was to verify these basics with their own department heads and swarm of sharks ... er ... ah ... attorneys.
My policy in teaching is that we are not there to take an inventory of everything someone has and report it or make it public knowledge. We only need to assure our safety and the safety of the patient.
This is a very brief description of how I handled this, and it is only how I did it. I know that there are emergency workers that are going to grab and turn over everything they find at first sight or knowledge, and there are some that will run and hide until all is clean. Myself ... If I am capable of maintaining control you ain't going to get it. If need be I will unload, but I will not give up to anyone but my choice and/or under my conditions.