George definitely had the Viet Minh in mind during ANH. George was way more recently out of college then and the war had just ended. Luke's role in the final product goes from all kinds of serial sci fi ideas to being essentially a young man of military age who has little future available, but has no real stake in the empire winning. Even wanting to join originally, despite hating it, because he sees it as his way out, an inevitability. Only for the empire to butcher his family and make him have to contend with the reality of fascism. The rebels in ANH are not exactly the viet minh, but Luke is for sure meant to be a kid who joins SDS. Remember Lucas was drafted for Vietnam but exempt due to diabetes which was genetic, having killed his grandpa. So he was saved from joining something evil, by chance and a prior family tragedy.

Looking at the earlier drafts Luke is just not that kind of character. I think last second having to bail on apocalypse now! made him approach Luke from a different perspective.

Ondaatje, Michael (2005). The Conversations: Walter Murch and the Art of Editing Film. Knopf. p. 70. Originally George Lucas was going to direct ('Apocalypse Now'), so it was a project that George and John [Milius] developed for [American] Zoetrope. That was back in 1969. Then, when Warner Brothers cancelled the funding for Zoetrope, the project was abandoned for a while. After the success of 'American Graffiti' in 1973, George wanted to revive it, but it was still too hot a topic, the [Vietnam] war was still on, and nobody wanted to finance something like that. So George considered his options: What did he really want to say in 'Apocalypse Now?' The message boiled down to the ability of a small group of people to defeat a gigantic power simply by the force of their convictions. And he decided, All right, if it's politically too hot as a contemporary subject, I'll put the essence of the story in outer space and make it happen in a galaxy long ago and far away. The rebel group were the North Vietnamese, and the Empire was the United States. And if you have 'the force,' no matter how small you are, you can defeat the overwhelmingly big power. 'Star Wars' is George's transubstantiated version of 'Apocalypse Now.'

This is not to say it is a great allegory, I never liked the ROTJ part of it, it plays into bad liberal stereotypes about the Vietnamese