Has a “white hole” theory been advanced to explain anomalous star formation in Sagittarius A?
I'm going to say that the answer to the main question is "no", for two reasons.


The Introduction to this recent paper by Naoz et al. mentions a variety of different suggested models and explanations, none of which is based on anything like alternate cosmological models. (The paper itself argues that the apparently problematic distribution of stellar orbits may be an artifact of failing to account for the presence of binary stars, so that the system isn't really anomalous at all.)
It's not at all clear to me how an alternate cosmological model like the one you link to would be even remotely relevant to the details of star formation in the Galactic Center. In other words, I wouldn't expect anyone to be trying to explain star formation near Sgr A* using alternate cosmologies or extensions to GR (the star formation took place mostly well outside the region where GR becomes noticeably different from Newtonian gravity, so modifications to GR would be even less relevant).


As for the second question: we simply don't know the direction or amount of the central supermassive black hole's spin (yet).