Well, I'm inclined to say the reason for Ginjou's betrayal is probably one of the notes Kubo gave Narita. Ginjou blaming Ukitake would be logical from that given Ukitake was the one who gave him the badge. It'd also explain why Ginjou was so truly good while under Tsukishima's power. It didn't alter his personality. It took away an event that altered his base personality. Or rather, Tsukishima became the target of Ginjou's hatred.
To be sure, that is the perfectly logical explanation for Ginjou's background and behaviour during the Lost Agent Arc, and I don't doubt this is probably one of the few notes Kubo gave Narita regarding the backstory of the series. It's the missing gear on why Ginjou was so suspicious about Ukitake, why he didn't trust the Soul Society etc., so I do think it makes sense more or less (outside of a few areas where it needed to be touched on, but those are nit picks at this point).
But at the end of the day, this is Narita giving his twist on Kubo's idea, since Narita is the one writing the novel. Even if he is using information from Kubo, the manner that it is presented and the additional information given (in particular Tokinada's potentially involvement) is going to be influenced and decided by Narita now. That's what I mean that we would never know what Kubo originally intended for how Ginjou's past would be shown, since Kubo decided that he would not show it in the manga proper.
Of course, I do think the way Narita decided to display the information was pretty damn good. It not only explains the question marks that were left at the end of the Lost Agent Arc, but also provides a lot of great exposition and expansion on the side cast and one of the central villain's of the series, something that the main manga had all but abandoned by the final arc. An actual sit in where the characters talk about their past and bond with each other, while revealing important information and give some self reflection is pretty much an A+++ thing for me.
