Hi,
Depending on time, HMS may be automatically replaced by NVG as helmet feature. You still have the choice to choose one or another by asking the ground crew.
As for the Skhval, as said before it is a day optic sight. There have already been many discussions about that point but it seems ED will not offer a Ka-50 N (or Sh in Russian) version. I use a mod kindly developed by a user which increases the maximum contrast (as far as I remember) of the Skhval. It allows to get a kind of FLIR view and it is quite efficient (when you can manage to lock the target...).