I imagine flash will not be permitted during the competition. The flash can blind the dancers as they are spotting, and really put them off on their turns. It can be dangerous, and distract them, which can mean the difference between winning and losing! I shoot a lot of dance. My girls are ballerinas, so in-class observations, on stage in productions, on stage in competitions, and on stage in high school productions.
I try to keep my shutter around 320, 250 the slowest. I shoot wide open with a 2.8 lens, I have a 50mm 1.8 but I don't get close enough to use that lens. The lighting changes on me so much, I have recently started to shoot in auto ISO, and in TV mode, so that the shutter doesn't change, but the aperture will adjust if the spotlights give me too much light. I also do spot metering, so that the back grounds, and the rest of the stage don't influence the meter.
Canon 60D|Canon Rebel EOS T1i|50mm f/1.8|28-70mm f/2.8|18-55 f/3.5-5.6|70-200mm IS f/2.8 |600EX Speedlite