No. Sure the USSR supported people's movements abroad, but that's not imperialism. Neither are military alliances in themselves. There wasn't an export of private or nationalized Soviet finance capital in order to exploit workers elsewhere.
Yes. Look at the evolution of the polish border between 1939 and 1945 for example. USSR moved the entire country to grow its territory. Look the Prague Springue. Those are two examples of russian imperialism
Half Ukrainian half Polish territories got fights for control by the two new nation states at their creation. Is it supposed to refute USSR imperialism?