Good point on the dress rehearsal to get your shots.
If I am shooting an event as the official photographer I don't pay any attention to whether I am in someone's way or not. I have a job to do. I don't camp in the one spot for the whole show - I'm constantly on the move so you aren't blocking one person's view.
Many of the best angles are toward the side of stages - so work the whole area.
If someone asked me to be the official photographer for a performance and then expected to stay in a seat I'd tell them to go jump - they either want decent photos or they don't - if they expect you to stay seated they obviously don't place too much importance on the quality of the shots.
