Since none of you wankers responded to my query, I called the Pemi Ranger office in Plymouth and asked them myself:
Both Osceola Vista and Waterville Campgrounds are now officially closed. They can, however, still be used. Each is gated at their driveways, but one can park outside the gates and pack in to the campsites.
At some point, there will be a snowstorm large enough to close the gates across Tripoli Road at the Livermore Road trailheads. After that, packing in to Osceola Vista will become a longer walk.
For those wishing actual humans at their campsites, there is winter service at Hancock, Blackberry Crossing and Barnes Field.
Yours on the Trips,
--M.