I'm sure we're all familiar with the Soviet citizens welcoming the Nazis with open arms, only to turn on them when they were oppressed just as badly if not worse.
Has this phrase "open arms" any meaning? If it was "open arms" in the USSR, I haven't the foggiest what super-human amity they met in Austria and the Sudetenland.
In Galicia and the Baltic countries - two places where the population had every reason and some more to revile Stalin - the Germans were met grudgingly. Grudgingly is about the best they got. This of course has to do with the policies you propose to change, but let's not go altering history as part of our premise: the best the Germans could hope for IOTL, as alien tyrannical invaders, was sullenness.
I also like "if not worse". National extermination or slavery may
or may not be worse than life under Soviet rule.
But what if this wasn't the case? Not to say I'm making the Nazis "less evil" or anything; but what if they simply decided "active wartime is not the time to purge the undesirables in our new territories; we can do that once we have crushed the Bolsheviks."
In short, what if they actually had acted as liberators as long as the war was going in?
The problems of one totalitarian regime "liberating" people from another totalitarian regime ought to be self-explanatory. The best the Nazis could be was (what they were in the Baltic countries: more of the same, rather than destroyers of the nation.
There were plenty of people (active communists and Jews, to start with) who were not going to be reconciled to Nazi rule by anything. These people were going to begin a partisan war: there were Red Army men who had been caught in the kessels on the loose, and of course the mass of the Russian/Belarussian/Dniepr-Ukrainian population may not have liked Stalin or his regime but hated foreign invaders of their native soil - you had GULAG inmates signing up in 1941.
The Nazis deliberately confused their genocidal plans with anti-partisan activity (look at the Commissar Order) which makes the whole premise of waiting until after the war to finish the genocide difficult. The German army - officered by a class who had spent a couple of decades in an echo-chamber repeating to themselves their own militaristic values, manned by frightened young men far from home who had been indoctrinated to regard communism and Slavs as a bogey-man, and to change that you ahve to start in 1933 - was not going to win hearts and minds in partisan war.
The three big causes of death were the Holocaust, the savage anti-partisan measures, and mass-starvation. Mass-starvation is also still happening: you can't liberate food into Leningrad, and the Nazis were plundering the USSR to feed blockaded Europe.
The Nazis did gratuitously alienate the Galician-Volhynians and Baltic nations by barging into their countries, tearing down their briefly-raised national flags, and immediately starting to treat them like dirt. That could probably be changed (the Germans will still make an occupier every bit as high-handed, foreign, and authoritarian as the Soviets had been without actually remaining their Ukrainian collaborators how racially inferior they are), but given that for these peoples Nazi rule seemed the lesser of two evils anyway, that can get you at most a few infantry divisions earlier and no weapons for them.
Well under the Communists, the Ukraine was often left on a starvation diet.
This is so misleading a statement as to be hardly true. Ukrainians starved more than one time under the Soviet Union, however two of those times (Civil War and Great Patriotic War) much of the USSR was starving and the communists were not the only ones responsible.
The third was the Holodomor. During the Holodomor, brutal Soviet policies to reign in the truculent administrations of the outer parts of the USSR, collectivise agriculture, and export grain to fund crash-industrialisation combined with natural poor harvests to cause a gigantic artificial famine. Results: terrible death-toll, huge migration to the cities and to other parts of the USSR. Similar stories were played out at the same time across the USSR's black-earth belt.
By the late 30s, this was over. It was no consolation to the dead, but Ukrainians were eating as well as other Soviets.
The Heer usually had very little problems handling occupied territory. It was once the nazi party engine and ideology came into the picture that things soured. Keep the occupied territories under Heer control until the war against the Soviets are over and you will have much better management.
You will still have some atrocities, you will still have opression, but generally, the Heer wanted its stuff and no resistance, if it got that, it did not go out of its way to kill, maim or opress.
This is the same Heer that issued the Commissar Order, exterminated three-and-a-half million Soviet PoWs, besieged Leningrad, and conducted the anti-partisan war with help from ill-disciplined local auxiliaries?
The Heer did control Belarus from august 1941 to spring 1942 (when large parts of Belarus which had been under Heer controlw as turned over to civilian authorities). While brutal, the Heer occupation cooperated quite well with the puppet government of the Central Rada and with the anti-Soviet partisans, meaning the pro-Soviet partisans and anti-Soviet partisans spent most of their time fighting each other.
Local auxiliaries were often used to fight the partisans: that was there main use. As so often happens, the USSR behind the line became a huge and bloody civil war: nobody's suggesting that in IOTL every Soviet was trying to throw out the occupier. The partisans made no bones about robbing their food. It was a nightmare.
In terms of volunteer soldiers, even in the countries Germany treated well there was only a trickle. Fear of Stalin and his NKVD (who will go underground) won't encourage volunteering any more either.
Then of course there's the problem of
arming these volunteers.
I would note also that the Nazis did try using battalions recruited from Soviet PoWs on the frontline. They were so unruly that the Germans sometimes had to shoot at them. After Kursk, the Germans threw up their hands and sent them all to the west - where in spite of their fear of going back to the tender bosom of the NKVD, some of them mutinied anyway.
It's not throwing them into absolute poverty if it is no worse, or marginally better, than the previous regime.
A violent invader is never exactly the same as the previous regime: all else being equal (it decidedly was not) and with the best of intentions (the Nazis had the worst), quite a lot of people have wrecked houses and dead childen thanks to you.
Iraq was a a doozie, amirite?