When you ask players if they flash bothered them after the game, they say, "What flash? I didn't see any flashes." Even though the stands are FULL of parents and high school kids snapping away, shooting flash picture after flash picture with their digicams. And, I've shot a couple seasons' worth of flash pictures using balcony-mounted strobes aimed down at the court, as well as big games with another photographer's flashes firing.
Yes, flash can help lighten shadows and thus eliminate noise in the shadow areas. Flash can also be used to create dramatic rim lighting if you put your flash on one side of the gym,aimed directly down at the court, and you shoot from the other side.
For on-camera use with a slowish lens like that, the biggest problem is focusing; that lens, handy as it is, does not focus super-fast. Easiest way to get rid of that problem is to shoot at f/5.6 at ISO 1250 or so with flash, at your top flash shutter speed (usually 1/200 second on many cameras) and shoot from the stands on the sides, so the action is moving more or less left to right from you. SHooting from the baseline, much action is moving away or toward your position, causing a need for a lot of distance changes and constant focusing. Shot from the sides, the distances do not change quite so much or so rapidly.
Volleyball can be shot from the court ends, focusing on the net play--blocks and spikes can be shot from the court ends, or from a spot in the stands just above the net height, which will give you a clear view of both sides so you can shoot digs and sets and net play. From the back of the court standing at the center, you can pre-focus pretty well, but you will need high ISO and f/4 much of the time to get a shutter speed of at least 1/400 second to freeze most, but not all, movement of the ball on spikes and blocks.