Really Taboo ?

It was probably that way during the Korean War, but when I was little in the 1960s there were several mixed couples in my neighborhood. My neighbors, the Barbers, were an Army family, and the wife, Sakiyo, was from Japan and there were seven children. Her sister, Keiko, was married to another Army lifer, and they all lived in the same town. No one cared about them being mixed. They all were married in 1958. Sakiyo ran that family with an iron fist.
The Divine Genealogy Goddess

Of course it was, this was 1957, a time when bigotry abounded on both sides. This was directly a result of WWII, just like the film stated.

As for the Chinese question, it was virtually a nonissue, because there weren't any US officers stationed in China.