There's no question, they're definitely accountable for violations like this. I think they know that, which is why they have the monitoring and interview processes in place.
The question for me is, what's the mechanism for enforcing accountability down the chain.
Foxconn operates the plants, so what is the mechanism for incentivising them to comply? What penalties or sanctions do they face for violations? That's really the only way to get to the root of this, but it can't be financial penalties to Apple. That would create perverse incentives and moral hazard.