Dominate never had the manpower to wage conventional war, and it never will. Look at every single pre-published scenario with them as enemies - they use ambushes, sympathizers among imperial officers, dress in enemy uniform, and do every dirty trick in the book.

Not that they are the only ones in the galaxy who fight like that, sure.

What I've found particularly useful in getting players out from under the thumb of command is to not drop them into the middle of an all out war in which the whole regiment must remain together or die. For lack of a better term, welcome to "Spaceghanistan" where the rebels are in hiding, the locals aren't the trusting type, and the players are the first true Imperial presence in centuries outside of that one guy we all pay taxes to because they say we have to. My players get sent on long patrols, have to interact with villages, track down insurgent cells, find out what's causing the rebellion in the first place, and all with little more than a radio for the most part. Sure it can be sort of awkward at first, but it's lead to some of the funniest interactions ever where they ended up hating an innocent villager and thinking the leader of the local insurgent cell was their best friend ever.

I can agree with this up to a point, except that, at least in my eyes, America still WANTS to appear to be the good guys. I'm not over there, I haven't seen how we or they behave, first hand, but I am led to believe that American troops don't just burn every village, shoot every anyone else they see, and other atrocities (this might be happening, of course), but the Imperium of Man isn't that animal. They go in, carpet-bomb everything that is suspicious, and then bulldoze down the refuse with Leman Russ-shaped levelers. Unless they are severely outnumbered, I don't see them dealing with villagers, looking for insurgents, and such; that's the job for OH Inquisitor's Acolytes/Throne Agents. The Guard are a weapon, less than a peace-keeping force; more a piece-making force. This may very well be my own limited range of vision talking, of course, but if we have a Commissar who will shoot us for dereliction of duty, I can't imagine him not also dragging in potential sympathizers, beating them across the face with his bolt pistol, and then just shooting them, for failing the Emperor. Them or the Adeptus Arbites, if they haven't been wiped out, and then the Guard have even more reason to just kill everyone.

Yes, but smash, smash, smash does not for a fun game make, at least not all the time. Certain bits of fiction must be bent at the very least or the players' answer to anything that doesn't go their way turns into shooting it in the face. That's why my players have been outnumbered, "alone and unafraid" has become their unofficial motto and they are often the only regiment sent in for such things. They wanted to play scouts, so scouts they are, often days or more away from the closest support and supplies in an unarmored truck. Weight limits are strictly enforced and the amount of ammunition starts to dwindle pretty fast and the ways of replenishing it has been fairly difficult to come by. I'm not saying it's the way to play the game for everyone, but it can make a nice change from "Let's do the whole village" style play.

Well on certain planets I'm sure that not only are the SD strong enough to fight a conventional war, they're the ones trying to rip out the roots of hardliner Imperial forces. This is mostly moot since he's not playing against the SD but still, playing loyalist VCs against better armed traitors sounds like fun. When it comes to asymmetrical warfare there's more than enough room for it in various depictions of 40k. Maybe the area is too important to carpetbomb, and not important enough to deploy massive forces. Maybe the players CO is trying to be a glory hound, or whatever other various reasons to play it that way.

Either way it sounds like a blast as soon as I read " they ended up hating an innocent villager and thinking the leader of the local insurgent cell was their best friend ever." I thought of Sgt Barnes screaming "I caca dau vc! " And that was before fire quoted Bunny from later on in that scene. Sounds like just as fun a way to play the game as grimdark WW2. Whenever I watch Platoon now I get the slight urge to run a similar game.