What was the significance of the Russian cultural backdrop in "The Deer Hunter"?

I think that it also ties in with a larger theme in the film, one that was not necessarily intended by the filmmakers.

The Vietnam conflict was a pointless war that the US didn't win, and it was played out within the context of the larger Cold War between the US and the Soviet Union (with China also a player). The war was about fighting Communism. The irony is that the men who go to the war are Americans, but they happen to be of Russian descent.

In one scene, Nick is sitting on a balcony in a hospital in Saigon when a doctor comes to verify his identity. He is "shell shocked" and clearly suffering from survivor's guilt having been rescued by the helicopter while his two friends fell back into the river. The doctor calls him by the Russian name on his record. He doesn't answer until the doctor asks him if his name is Russian. He says "no, it's American."

The point here is that these were hapless, working class Americans from all backgrounds who were sent to this futile war to fight and suffer and die for the benefit of larger powers involved in an ideological and global economic/political struggle. The Russian Roulette isn't Russian, but its name makes us think of Russia. And it is a deadly game of chance that is played, ultimately, by people who exchange money as bets on human lives, much like the powers that control wars.