After calling the Manchester area chamber of commerce, I have found out that the situation is most likely as MTNRUNR called it: top half unplowed, lower half plowed because of the monastery i found out about only an hour ago. Looking at a map, the road rises to the ridge, where it splits, one route heading toward the summit, one toward the monastery. I doubt it possible that the monks allow themselves to be snowed in during the winter for safety and food reasons but they also don't have the hangups or needs that we do.
It is private property, so any activity on the road in winter would be at your own risk or should be cleared with the clergy!
EDIT: After further examination of the map, there are two parallel roads that rise to the ridge (Bentley Hill Rd & Skyline Drive, both off VT7A), so it is possible, and downright likely, that one remains unplowed. If anyone passes by this area in the near future, keep an eye out for me.