I think it's important to be clear that the grievance that's being prevented here is if the tribunal has ordered the employer to discipline you because you have been shown to be a repriser. So you're not the whistle-blower; you're the person who has reprised against the whistle-blower. That's what that prohibition is doing; it is preventing the repriser from going down a path of grievance.
If you're the whistle-blower and you feel that the tribunal's decision is inappropriate or insufficient in some fashion, the act has put in place a judicial review mechanism through the Federal Court of Appeal.