I'm really struggling with this reading. The rebels aren't space communists trying to save their homeland from the encroaching Empire, they're fighting to restore the republic that was the precursor to Palpatine's totalitarian regime. If you allow for the sake of argument that they represent the Viet Cong, then the story of the first movie is about how a handful of heroes, some of whom were defectors from the Empire, were the ones instrumental in the first major Rebel victory, which is a bizarre kind of Great Man Theory/white savior complex that I imagine the Viet Cong wouldn't have appreciated.

Also the later movies make it clear that the fall of the republic and the rise of the Empire was almost entirely due to the machinations of one man, Darth Sidious a.k.a. Emperor Palpatine, which again points to a Great Man Theory of history and doesn't align well with the real world, where the rise of the U.S. as an imperial power has more to do with structural forces that serve the interests of the capitalist class.

I'm not saying Lucas didn't intend it to be about the Vietnam War, but I'm saying that if he did intend that, he didn't include much in the movie that supports it.