Well, it's a good question. I have the opinion that the way the helicopter is flown depends highly on where the pilots come from. S61 is a helicopter designed for the Navy. In the Navy pilots don't fear to fly near the sea surface. While Bell 412 is more for Army operations. And you can notice it if you analyse how these helicopters are flown.
I'm from the Air Force. In the AF we see helicopters as another type of plane. We use to think that if you don't have contact with the ground, the higher, the safer. Flying at 200' feet is inherently dangerous. An autopilot failure with mode disengagement can make you lose more than 100' feet. Not mentioning a tail rotor failure.
I think that at night, even with NVG you should keep 500' except when in final approach (being this approach to a helipad or a vessel). I don't think NVG gives you much clues when flying over the sea (this is my experience).
I'm staying out of this one!
