I think the Brazilian Astar is a special case. Having done a fair bit with AS350s i can tell you that they dont get ground resonance without some serious issues mechanically, landing gear dampers with no oil, skid springs flat and bearings shot in the AVA.
They certainy dont shake apart without having a few days of increasing divergent ground resonance that is either handled by the pilot or sorts itself out as the rpm changes on run up or pulling the throttle to idle.
Should have been dealt with way before it got to that point..
As for ground runs im with Robinson, pilots only unless the aircraft is secured to the ground (not for multi blade aircraft through, cant tie them down)
The other issue no ones mentioned is trying to get some lazy ass pilot to do ground runs because "theyre so busy".
Sometimes its quicker to do it yourself!