Actually, I should clarify, I enjoyed Redemption Corps too, when I read it. The action was fun, the rivalry between the protagonist and the Commissar in training was interesting, and genestealer infected Orks were good antagonists. Its portrayal of Sisters is probably the one thing I dislike about it, but apart from that, enjoyable book.
As for the Cain novels, I got the impression that the examples of squad relations we see there are allowed to carry on, in part, be due to Cain's unusually liberal attitude. Normally it's the Commissar's job to root that stuff out, yet he's quite clearly not inclined to do so. I mean, some of them are implied to have made babies, yet Cain maintains his rapport with the troops and is still said not have executed anybody. If a proper Commissar was assigned to that regiment, things like that would most likely be violently rooted out and punished.
But, as you mentioned, a healthy dose of salt is probably nedded for some aspects of the Cain novels regardless.