Parkamoor has an off-grid house half way up it – I think it’s an Airbnb or something now. The only way to it is to park at the bottom (High Nibthwaite) then the farmer / landowner takes you to the house in a 4×4 for your stay. So that track, from the bottom up to the house, is definitely in regular use plus the Kankku lot use it all the bloody time.
The rest of it, from the house up and over to Grizedale where it comes into the forest at Heald Brow should just be normal bridleway. A lot of that bit on the western edge of the forest was closed / blocked for a long time after one of the big storms and certainly most of it was singletrack, not accessible to any vehicle (which is part of the reason it was blocked for so long).