US executives can be compelled to testify truthfully under oath. There is no "Chinese law compels me to keep this secret" defense to perjury charges in the US. If credible evidence emerges, Apple executives will eventually be forced to admit whatever they know. The only viable strategy here is to have a broken system and plausible "not know" it's being exploited, but that's a very fragile approach (technically risky, vulnerable to whistleblowers) and it only works once.