One of the most common failings to doing risk assessments is to only do half a risk asessment. That is not to look at ALL the risks, and the changes that occur good and bad.
I have been brain washed into the UK system, so I know that leaving rotors running is not allowed. But taking a look at the picture, the use of the truck top means that no third parties can reasonably get to the rotors. The pilot and crew seem to be restricted to working close to the airframe so they cannot get to the rotors either. So where is the risk from the rotors running, so long as the cotrols are locked in some way?
Of course, in the UK the H&S Nazis would get you for working at height without edge protection, but let's not even go there..............