From what I have read, the odds are rather high that the people who cook, wait tables and serve at many, perhaps most, Chinese buffet restaurants are brought here illegally by snakehead gangs, and are working off outrageous fees for being smuggled in. Most of their income goes to their parents back in some rural hamlet in China,. or to pay off the snakeheads.
I have not noticed anyone who speaks much English or is not obviously Chinese working in such places. I suppose they could be Japanese or Korean or such, but I tend to doubt it.