The answer is, generally, no, because at non-meal times the FAs snap the curtains closed, and you can't get to the lav on the right side of the plane in the area between D1 and PS unless you unsnap them, which could cause real trouble for you.

During meal times, when the curtains are unsnapped, and carts are in the aisles, you can get to that lav, and the FAs have not said that I could not use it then.