First of all, China does not recognize dual nationality, that is, Americans who cannot have China nationality. To put it bluntly, as long as he is an American and has American citizenship, he can't acquire China citizenship unless he renounces American citizenship. So your first question doesn't hold water.
Of course, it is also possible that he was originally an American, and later gave up his American citizenship, joined China citizenship, and became a China native. Then legally, he is no longer an American.
There is only one thing you need to remember here. Only China lawyers can participate in the defense as lawyers in criminal trials.
As for those other defenders who enjoy less rights as defenders than lawyers, Verolau has attached relevant legal provisions, so I won't explain them any more. However, you should note that lawyers' rights are more about reading, reviewing case files and investigating evidence before the trial, and there is not much difference in court defense. You can leave me a message if you have any questions.