I am entirely unqualified to comment on rotorcraft and icing or snow.
Your point on judging height and terrain over snow covered ground does remind me of the 1979 Air New Zealand DC-10 Mount Erebus crash. The pilots were in VMC but still flew straight into the snow covered mountain. All souls on lost on the tourist flight. It was a really big deal for Air New Zealand. A national carrier. All charter flights to Antarctica ceased and did not resume again for another 34 years.
"Passenger photographs taken seconds before the collision removed all doubt of a "flying in cloud" theory, showing perfectly clear visibility well beneath the cloud base, with landmarks 13 miles (21 km) to the left and 10 miles (16 km) to the right of the aircraft visible"
- Royal Commission Report, para 28