Yes and no. Technically that rear sight is a Yost-Bonitz rear sight that was made without a notch. Back when that pistol was done in 2005 or so, Yost-Bonitz was the source for that part. Ted Yost had some sights with no notch cut into them as a result of a tool failure. John acquired some of them for me, so the notch could be cut to match the dimensions of the BoMar rear notch. It was paired with a front sight that John made to duplicate the front sight on another Harrison pistol that had a BoMar rear. My eyes are unusual in that small notches and thin blades work very well for me.
I am not sure of the details, but Ted Yost and John came to some arrangement, and John now offers his version of the rear sight. That sight design has led an interesting life. Back in 1997, Robar put a version of that sight on my first custom 1911-pattern pistol, a Colt Lightweight Commander. As Robbie Barrkman and Ted Yost have crossed paths professionally many times, I am not sure where the actual rear sight design originated.