It doesnt take Hitlers death to make this work for a time at least. Say Rosenberg manages to push his views better prior to the invasion. In early 1941, Hitler isnt yet insane, in fact, he remains rather quite pragmatic and may accept a temporary handicap for long term gains.
Under a variation of the Rosenberg proposals, Vlasov could have his place. His "light troops" would in fact recieve many dangerous/suicidal missions of course to keep their numbers manageable. What a better way to depopulate than make the enemy kill himself for you? Those of these missions that actually succeed would be used as propaganda to keep the other "Free Russians" going.
At the end of the war, though, it is to be made certain he has little influence and no real power to oppose Germany. Then Germany shall annex several areas that were promised independence, but accept in others to set up puppet states for the time being, and focus their eastern colonialisation plans in stages. First the baltic states and Beylorussia, and only when those are German, once the weakened poles and ukrainians who have served as very cheap labor in the meantime are exhausted, will these territories be colonized as well.
Its probably more realistic and efficient that way than their OTL approach of "Hey, lets just send 10 million germans all over the place, as fast as we can!"