I am not aware of any evidence that LHO expressed anything about Vietnam. My reasoning is that it was a news topic and LHO appeared to follow some of the political news. And that he most likely had a similar view to Castro’s view about it. It’s even likely that LHO heard Castro’s view on his radio while listening to Cuban broadcasts.
It seems like I have read that LHO had a photo of Castro hanging in the New Orleans apartment. And that Marina added a photo of JFK that she got out of a magazine.
Marina said he used to sing songs to "Fidel" (whew) and wanted to name their first child after him (this was when they were in Minsk). After the Mexico City incident, she said he soured on Cuba and didn't talk about it.
But of course, our conspiracy friends will say all of this was an act. He was really working for US intelligence and pretending all of this. Double whew, that's some fantasy. One of my favorite writers, Saul Bellow, once said: "A great deal of intelligence can be invested in ignorance when the need for illusion is deep." Thus the thousands of conspiracy books being produced. And read.