Can a wideout swing his arms before the snap ? I noticed most wideouts around here go into a boxing stance and freeze. Others hang arms at their side. Once in a while someone has a swing . While I never had the opportunity to make a ruling , I believe I'd call a dead ball/false start.

What's the advantage gained? If it wasn't abrupt and didn't pull the defense offsides I'd let it go. Then again, they keep me in the middle.

This is no different then a lineman pointing out a blocking assignment with his offhand. Nowhere does it say they cannot move, it says they cannot "simulate" the start of the play. I would say what you are describing is not "simulating" anything, so no foul. Now if his arms are still and he snaps them up or something like that just before the snap, we may have a problem.