It's race in all but name. They actually get around it by specifying everything about a person other than race, like skin color, accent or language skills.

If they need a Viet person for a role in a Vietnam War movie, they'll cast for "native or fluent Vietnamese speakers". Of course it's entirely plausible that a black guy is a fluent Vietnamese speaker but auditions are very subjective so good luck proving that the black guy played the role of NVA Soldier #1 better than the actual Vietnamese guy.