I tend to forget that the Vietnam war was not just an "American" war, but also countless of nations who partook in it. But how were S.Vietnamese troops treated after the Americans departure and the eventual fall of Saigon and how are they treated now?
Immediately after the Fall of Saigon, the South Vietnamese including the armed forces were treated quite well all things considering. Most returned home after the fighting ended as as the NVA aimed to restore order.
During the next few months, former members of South Vietnamese regimen (not only military but civilian, including those who worked with the US in civilian roles) were required to register with the new gov’t and were informed they would need to take part in re-education. They were told rank and file would only need to attend for a week or so, while high ranking leaders a month. This is in 1975, but the last people to leave the camps did so in the 90’s (close to 20 years in camp).
The camps were very basic camps where prisoners (which is what they were) attended re-education sessions and often did forced labor as well. Food and medical care was scarce (as they were on the outside as well) and punishment was often harsh. Prisoners with good standing could have their families visit once every 3 months and they could bring the prisoner food (which was often a necessity for survival).
Now, experiences did vary considerably. Those not considered a threat to the new regimen were released relatively quickly. Those considered threats would spend more than a decade there.
Outside of the camps, there was little discussion or recognition of the old regime. That was the old, illegitimate, criminal “puppet government”. Service to the old Republic was not recognized including any military service. South Vietnam military graveyards were locked up. Any signs of the old regime removed. Street names that were regarded as counter-revolutionary were changed.
There are plenty of people living in Vietnam today who had ties with the old regime (I have extended family in that situation). You pretty much don’t talk about it. I think the current government is much less sensitive about it now that it’s almost 50 years later. It’s not like you can’t talk about life pre-1975. But it’s still not discussed much, particularly among those on the losing side.