User blog comment:Xilinoc/Ch. 596 - Rubb-Dolls 3/@comment-493809-20140911125643/@comment-493809-20140916062738

I would argue that Yhwach is immune to the Hollow-based weakness, if for no other reason than the fact that he had started recruiting Arrancar and (seemingly) giving them Quincy powers. It may be that his soul-split ability's healing function can restore the heart of a Hollow (the two Quincy Arrancar we've met have been in uniform, so to my knowledge the locations of their holes remains unknown). That might also explain why a Hollow's powers are so dangerous - Quincy are still alive, like Humans, but the power could be torn between their existence and healing the Hollow that attacked.

Also, some more (admittedly flimsy) evidence - Combined Zangetsu has some superficial similarities to Released Starrk, including mask location and fur trim.

Again, not likely to be true, but it's fun to imagine it.