To deal with the specific question.
It depends on the circumstances - weight and performance of the helicopter, conditions etc.
I"ve not seen the clip you describe but considering the way you describe it then it would certainly have been subject to at least one Permission from the CAA.
I'm certain that one of their requirements would have been the ability to safely fly away in the event of a single engine failure (taking into account the height above the water that was required for the task and any available drop-down), more likely it would require the helicopter to be flown at weights that allow single engine hover.
OH