Yes, military tribunals are consistent with international law, because they allow for justice. Even in international court, the person is not tried in the courts of the country against whom they committed their crimes. Rather, they are tried in the international court that is specifically set up for that purpose. The military tribunals properly deal with these offenses against the United States.
Suspected terrorists should be tried in some other form. Military tribunals govern military personnel who agree to be governed by them. The Federal government should hold trial for suspected terrorists, as this would be a more fair form of trial proceedings. Although the military serves a great purpose, the laws which govern it are specific to it, including military tribunals themselves.