I'd argue it was a vassal state, not occupied (per se) at least from the 1950's onwards. Yes, the soviet troops did station in Poland, but the beatings were administered by other Polish citizens.
No. I mean the support USSR received from USA after the German attack.
A third of trucks used by the Red Army where US made
A third of soviet airforce was US made. US also sent a lot of high octane fuel needed for the airplanes.
A significant amount of food.
It is very likely that the USSR would not win if not for the US material support.
The USSR was perfectly capable of wrecking havoc on itself without the fed.
While the Soviet evacuation of it's industry to the east was impressive one must not forget the massive aid the USSR received from the western allies.
The vast majority of wars have been won by the party with stronger economy. There are of course exceptions. Especially when the theater of operation is on the other side of the globe (i.e. 1776)