Board Thread:Roleplaying/@comment-1734134-20190906112145/@comment-1734134-20191117023750

"Really, you act as if the way Commissars go about their business would not affect some nobody PDF grunts, but even the most hardened, tough-as-nails Guard Regiments know to respect and fear the Commissars. Cadian Guard? They serve dutifully under the watchful eye of Commissars. Armageddon Steel Legion? They are run in their entirety by a Commissar."

I'm not saying it won't effect them; what I'm saying is that these troops aren't really too inclined towards outsiders, especially given the near total breakdown of Imperial CinC. There's also a difference between being tough and disciplined; as you've probably noticed, the left-behind forces aren't really disciplined. You would find the Commissars authority would go much further in the urban areas where the Guard are still in control and have not descended into near anarchy. Even then, the Governess is basically allowing local military leaders to rule however they see fit as long as they don't turn their guns on the other Imperial forces.

Catachans also regularly frag their Commissars; a point made on Lexicanum (this was even part of the 40k ruleset at one point).