No, actually it is not. The flywheel itself is balanced. It is put on a machine, spun, vibration is calculated, and weights are applied as/where necessary. Just like balancing a tire... Or a flywheel/flexplate on a car... It does nothing to actually balance/reduce engine vibration, like a harmonic balancer (crankshaft pully) on a car. Those are comprised of 3 pieces; the inner piece that slips/presses onto the crank with a bolt, a strip of rubber that goes around it, and lastly another piece of steel over that. That last piece has grooves machined in it for the drive belt to ride on. The rubber in the center absorbs the engine vibrations that travel through the crank. Some trucks even have a harmonic balancer on the rear axle's pinion shaft to absorb driveline vibrations. Same principle.
The balance shaft inside the engine is what reduces the engine vibrations. It is just a shaft with a lobe on it(specially calculated for weight) that is timed with and driven by the crankshaft. Many automobile engine have a balance shaft (GM 4.3L v6, certain Honda 4cly engines, etc... Using such methoids pretty much eliminates the need for a harmonic balancer, although MFGS still use them on certain balance shaft engines.
I'm not looking to start a fight. I just like for proper terms of componants to be used, and to edjucate people. However, if one of those weights where to come off, the engine in a Warrior (or any other atv) would vibrate like a bitch. lol