I had no trouble walking up the Nab from the public road on 15 April 2016. Here is what I wrote at the time:
Parked on the verge near Dale Head Farm then walked up the track towards The Bungalow for 300m then south across the lower slopes of the fell to a ladder stile over the wall. From there a distinct trod leads to a gap in the next wall. After crossing this second wall, follow a fainter path south along the west flank of the hill for approx 400m then turn northeast to reach the summit. I didn't see any prohibiting signs and, although the road is private, the fellside is Access Land. I returned by the same route; took about an hour up and forty minutes down. This was a solo ascent to tick off The Nab. Slight breeze, cloudy, odd shower.
PS: I didn't see any deer.