Yes...all the real world wars occurred in 616. It is just that with the sliding time scale people's ages shift along with it so people who served in Vietam would not be old enough to serve in Vietnam. For example Flash would be the same age as Peter....late 20s...someone in their late 20s would have been born in the 90s....decades after the Vietnam war ended. So they are retconning several characters military service from the real war to the fictional war.
For reference...
https://marvel.fandom.com/wiki/Sin-Cong
https://marvel.fandom.com/wiki/Siancong_War