Phrogman - our SOPs are as you suggest, overwater letdowns are conducted the same way ie as if you were IMC even if you are VMC at night on NVG. That way none of the safety calls, rad alt bug setting or NHP monitoring of descents is missed and the NVG are just used to assist in lookout. I have also seen many guys need the assistance of the NHP at the end of an NVG biased approach over the water.
Each pilot has a steerable spot light and there are 4 further flood lights (2 on the underside of the nose and one in each sponson) and the winchop has a steerable spot as well which he can use to assess tip and tail clearances as well as illuminate the winching.
Almost without exception, the winchop will be on white light for winching but if he can see better with NVG (winching through trees is one situation I know it has been done) then he will use them.
Having concentrated greatly on the use of NVG and lights, it is worth highlighting, from my experience, that the most dangerous time, especially over the water, is dusk; there is enough light to fool pilots into thinking they can use day techniques but not enough light to actually do so and it is often the inability to assess accurate rates of closure that catches them out. Mountain flying at dusk is equally fraught with danger, especially if you are trying to make an approach to a feature looking into the setting sun - unaided it is too high contrast and the terrain is in deep shadow and on NVG the picture is just burnt out!