That's not really an apt comparison, given that Stalin never ruled Poland, only had large influence on it. United States has a large influence on many states today but no one would really even consider similar arrangements with, say, JFK from CivRev2.
I would actually find Poland led by Nicholas II to be a pretty neat idea, though that is a fairly subjective topic. Delineating, for instance, that Bismarck is not a valid alt. Polish leader for reasons, why any future Han-Tang emperors wouldn't be fit as alt. leaders for Vietnam even though they are a part of Vietnamese dynastology like anyone else... it's simply my own opinion that I do not see Vietnam as an entity during that time any more than I see Caesar as a leader of France. But all that is, as I said, a subjective assessment.