Frankly, if the Germans were invaded, it wouldn't excuse starting to use a phrase the traditional Nazi's used, even if the people invading were monsters. In the same way that the swastika is an appropriated symbol, but no longer represents that because something came along that carries far more ... historical weight, shall we say.

If someone invaded the South of the US, I would not be okay with the US starting to use wildly well known confederate slogans.

Also, you just said the Russians are the heroes you were referencing that were defending their country from imperialists who are doing all that bad stuff. I know that isn't what you meant, but that is what you said. Might be worth an edit, if you care.