Victors write the rules. Hence why Hitler is often painted in a much worse light than Stalin and Mao.
Stalin and Mao don't hold a candle to Hitler's regime in terms of crimes against humanity. This is no way means their criminal regimes were good, just the lesser evil.
I am curious how everybody would react if relic decided to add them in some form
They already are. OKW is based on the Army Group B which were the offensive forces utilized during the Battle of the Bulge and contained a total of 2 SS Panzer Corps in their order of battle.
But I would not be surprised if the single player looked to stir controversy in the same way the CoH2 storyline did in places like Russia.
I don't think Relic decided to stir controversy, I think they genuinely didn't bother to do actual research and just read some German interpretation of events that was published in the USA during the cold war and accepted it as the truth.
If they do decide to hop back into ww2 again I really hope they do their job properly this time.