If his Mexican wife is moving back to Mexico, why would this not apply?
People who can make importing your household goods without payment of taxes on foreign trade are:
Mexican students or researchers.
Residents in the border area or region.
Or Mexican immigrants repatriated or deported.
SOURCE translated by Google: http://www.sat.gob.mx/aduanas/pasajeros/Paginas/Menaje_casa.aspx