How many million gallons of jet fuel ever been hand pumped...machine pumped into a running helicopter by the pilot during bush operations? Do I know anyone that has had any kind of problem as a result of that...or taking a walk over behind a convenient bush to leave a soil sample for the locals to ponder....or just to geek on a tailboom or shut a door? Not one. I have heard stories...pariticularly with helicopters in snow....especially if they did not have snowshoes on the skids.
Legal? That might be a great argument. Wise....that is another argument. Do it....yes..but now that I am older and wiser....I do it with great trepidation.
You can what if this to death...but the totality of the circumstances are the key to it. If it is getting a bit snowy, sunset is coming, it is -45F outside....shutting down might not be the right answer. Setting on the beach next to the beer stand and lined up double breasted boobie birds....no brainer...shutdown every time. (....and pray to the great Helicopter Wizard that for once the starter will go on strike!)