(a) The following employees are not subject to this subtitle:
(1) a person employed as a domestic worker or a casual worker engaged in employment incidental to a personal residence;
(2) a person covered by a method of compensation established under federal law; or
(3) except as provided by Subchapter H, a farm or ranch employee.
(b) An employer may elect to obtain workers' compensation insurance coverage for an employee or classification of employees exempted from coverage under Subsection (a)(1) or (a)(3). Obtaining that coverage constitutes acceptance by the employer of the rights and responsibilities imposed under this subtitle as of the effective date of the coverage for as long as the coverage remains in effect.
(c) An employer who does not obtain coverage for exempt employees is not deprived of the common-law defenses described by Section 406.033, but this section does not reinstate or otherwise affect the availability of those or other defenses at common law.