Having seen the bridge close up, there would be plenty of room. BUT if this pilot is blatently braking the rules, what other stupid things is he/she doing. Flying under the bridge may or may not be dangerous, but the pilot's attitude is dangerous. Dont care much if he/she kills themselves. Do very much care if he/she kills someone else or leaves kids without a father/mother.
As for disruption, a light helicopter will do very little damage. But it would take a civil/structural engineer a while to prove it.