Up here in Canada our winter's average between -25C and -30C. ...
In Southern Finland we have -15 C - 20C . In few days it may be -30C.
500 km to inland and to north we have perhaps those numbers.
Cold air is dry. Air moisture may be out 90% but when it is warmed upp tp +20C , the room moisture may be 20-40%.
Never heard that hive are too dry. During hard frost ice crystals are inside the hive on cool wals. Bees keep their own tempetature in their ball.
I have heard from two professional beekepers that if you give dry sugar to bees on winter, they may die lack of water. When I have feede pollen patty at spring to bees and if they do not get water outside larvas will be destroyed and chalk brood burst out. I am goin to drink bees next spring.
Moisture to the hive comes from the respiration of bees when they consume sugar. When it is -20C, the upper ventilaition entrance is stucked with snow crystals.
But if you keep them in too moisture, they will get a nosema.