Yes, it's common practice to perform due diligence and regular audits on your manufacturing chains, especially ones that yearly get news articles about how many of your workers commit suicide.
Why would they audit if they're not held accountable? This starts to become chicken and egg, it sounds like. Perhaps best to just pick the party that should be responsible and then move forward.
Apple could audit them, but is it common practice to do so? Otherwise this seems like a case of hindsight is 20/20.