So culture shock is not a significant factor in the raising of regiments.
Aye, they try to put regiments where their specialties can be used for maximum effect...but this IS the Imperium of Man. You're going to have Valhallan on desert worlds and Catachan troopers slugging through Hives. That's just how the dice roll. Or how the Adminstratum clerk handles the cogniators, I guess.
I was wondering about possible friction between officers and feudal-world Rough Riders, who until they were levied were part of the upper class of their world, be it absolute ruler or just the owner of a feudal estate, but I guess their training could grind that out, too.
You get a lot of this cultural conflict. Couple of examples stick with me from the Gaunt's Ghost series (very mild spoilers for Sabbat Martyr
and His Last Command
, be warned!):
So in Sabbat Martyr the local planet the Ghosts are fighting on have a restriction on flame weapons: within the grounds of the city, only officers of the local PDF could use flame weapons. The Guard stationed on the city had to do without.
I can only assume this flew because the local PDF's leader (a Marshall) outranked the Guard's commander (a colonel). I'm sure if it went the other way around, the Guard commander would have told him to shove it. Barring the need to play nice and keep everyone happy.
Though, in the end, the Guard commander countermanded the local laws and supplied his troopers with flame weapons when things started getting bad, anyway.
In His Last Command
, a HEAVILY aristocratic light support vehicle regiment did some unorthodox decision making: when things got hot their commanding officer left the field of battle because he was too valuable to lose. Well, that didn't sit well with the Commissariat, and one commissar mentioned that, in all likelihood, their commanding officer would be shot without trial for abandoning his post.
So that's one way it could end. Either they shut up and place nice, or face the consequences. The Guard isn't exactly adverse to stepping on some toes (or necks!) to get their way.