[@Flamelord]
Well, they'd be Space Marines. So not incorruptible, but... fairly hard to corrupt. I mean, what are you going to offer them? Money? Weapons? 

Regardless, you might be able to get something in eventually. But all it takes is one or two failed attempts to start a war. Cuz once you're caught trying to smuggle nukes into the Imperium, you ARE going to get interrogated.