In regards to U.S. Law to be employed by the government. You would need to be certified to DoDD8570 specs. Here is a baseline to understand what certifications are required depending on the role you are looking to be gainfully employed. These mostly require being GIAC certified among some of the other certifications.
In regards to becoming a "Certified Ethical Hacker", you would need to pass the CEH test by the ECCouncil.
As for laws protecting "Ethical Hackers", there really isn't any. The law which applies is mostly for prosecuting criminal acts. Not really for the protection of the security consultant. This law is called Computer Fraud and Abuse Act in the U.S. and in the U.K. the Computer Misuse Act 1990.