The problem with a Soviet-backed Israel is how do you reconcile the atheist Soviet Union with the religiously founded Israel. Don't forget that the Jews believe that Israel is the Promised Land mentioned in the Bible.
But not all of those who founded the Sionist movement were religious. At the early years of the XX century, there were proposals of founding this state in Uganda or Patagonia, for example. "Palestine" was prefered for many reasons, not all of them religious: Palestine was, both for religoius and non religious Jews, the place of origin of the Jewish culture and nation. There were even some ultra-Orthodox Jews who were
against the creation of the Sate of Israel, because they considered thet this state would only be established when the Messiah came.
Still, I agree that this situation would cause problems. For the Soviet official doctrine, the Jews would stopped being oppressed only when the capitalist system had fallen, and communism had been adopted everywhere. Jews should fight for this goal wherever they where. When this was achieved (or, "in order to achieve this"), religion would/should be abandoned. Traditional cultures (like the Jewish culture) and languages (like Yiddish) would survive for quite a while, but they would only be folkloric relics of the past, destined to dissapear in the long term.
The problem with Sionism (for the Soviet official doctrine) was not only a
religious one (as not all Sionists were religious); it was that it gave Jews, both in an out the Soviet Union, a goal which was
different from the one the Soviets had established. The idea that Jews in the Soviet Union should consider themselves a separate ethnic, cultural and/or religious group who should try to emigrate to Israel or, at least, hold a certain sort of "loyalty" to this state, was something that a totalitarian state like the URSS couldn't accept, as totalitarian states tend to ask their citizens to be
entirely loyal to their regime.
This is why a less toatilatarian Soviet Union might make this scenario more likely. However, even if this isn't the case, we shouldn't discard the possibility of an Israeli/Soviet alliance. After all, diplomacy is ruled more by pragmatic reasons than by ideology. I mean, the US and Saudi Arabia haven't got much in common ideologically, and that doesn't stop them from being allies.