A person should always feel obligated to report illegal behavior, no matter who the offender is. No one should just sit back and allow illegal behavior to happen, and no one should be afraid to report such behavior, no matter how big or small. Corporations are no different than individuals when it comes to this.
If a worker has completed an infraction in the company's name, then the company has the duty to report it. If a worker has completed an infraction in their personal life (i.e. nothing to do with their work at the company), then I think it is down to the company to decide.
If Subway knew about Jared Fogel's involvement in child porn and child sex trafficking, and whatever else he was doing, someone should have reported it. If nothing else , if they had no compassion for the children, they had to know that it would get out eventually and that it would look bad.
I do believe that a company is responsible for reporting illegal behavior of its spokesperson or any employee of that company. Individuals and groups hold a responsibility of reporting illegal actions or behavior of its members, so it should be no different for companies. To grant them immunity to this simple moral obligation is wrong.