Falling snow is not icing condition in (at least) 99.9% ot the cases.
Falling snow and limitations in flight often refers to risk of flame out if lot of snow has formed on roof of heli or at engine inlets. This could make the engine flame out if a lot of 'clogged' snow comes loose and goes into the engine.
Bell jetranger: snow defelction plates should be mounted.
MBB bo105: min 800 meter visibility. Possible to mount continous ignition probably allows lower vis. (dont know the civilian POH to 100%, but flew a military version).
AS332 super puma: no restriction in snow visibility, but about how long time ground run as allowed without check on roof(max 20min in 400m or less)