The following persons are exempt from the license requirement imposed under this chapter:
(1) a person in the service of the state military forces or the United States while the person is operating an official motor vehicle in the scope of that service;
(2) a person while the person is operating a road machine, farm tractor, or implement of husbandry on a highway, unless the vehicle is a commercial motor vehicle under Section 522.003;
(3) a nonresident on active duty in the armed forces of the United States who holds a license issued by the person's state or Canadian province of residence; and
(4) a person who is the spouse or dependent child of a nonresident exempt under Subdivision (3) and who holds a license issued by the person's state or Canadian province of residence.