I was always a bit of a proponent of training and qualifying of engineers to carry out ground runs within the organisation that I used to work for. Apart from simulator and aircraft training I would have suggested that collective remained locked down and consideration should be given to limiting runs to ground idle.
On the subject of ground resonance, I can't help thinking that anyone who starts up a modern helicopter that has just come out of maintenance and then experiences 'ground resonance' should just shut things down as quickly as possible - I certainly wouldn't want to go flying in it!!
Cheers
TeeS i