My game, I'm the referee, I'm asking for state paperwork, and absent that, I'm still allowing the interpreter to stand wherever it's best for the deaf player.
However, before I leave, I'm telling the head coach, and the athletic director/site director, to get paperwork from the state for the next game.
I'm also getting the player's name and number before I leave, and when I get home I'm emailing the information/situation to my local assignment commissioner who is the liaison between our officials and the schools/state.
I can guarantee that my assignment commissioner, my local interpreter, and my state interpreter will back me up 100%. I'm also willing to bet that the state will probably back me up as well.
Again, the usual caveat, when in Rome ...