Yes, in
Pharos Sanguinius and Kurze have a long turgid dialogue where Sanguinius claims he can rehabilitate Kurze from essentially mental disability and make him spiritually whole. This is well after the start of the war.
Kurze makes his contention that the Emperor designed him to be the way he is, and all the bad things he did were the Emperor’s intention. That’s always been his story, since the Index Astartes days before the Heresy series.
Meanwhile the recent Raven Guard supplement gives them a unit that fights slavery even in the 41st millennium. We know from Angron and Nuceria that the Emperor could have easily shown up before the victory of coral and done a deal with the slave masters on Kiavahr.
codex supplement raven guard wrote: The 6th Company holds the honour of upholding the Primarch’s lifelong battle against tyranny, deploying to thwart the ambitions of despots, demagogues and false prophets who would shackle Mankind with chains of servitude.
The official situation of these corax is a lot like a good person being born under an evil regime and joining the security forces of that regime. meanwhile even the same evil regime occasionally prosecutes it’s henchmen for war crimes, in order to disassociate itself from things it orchestrated, the way Kurze claims to have been scapegoated.
Almost nothing has to change for your scenario
OP. A coin flip would explain it