Yes. If they have a right to be here illegally, they have an attendant right to use drugs illegally. Per NAFTA.
Forget about NAFTA. Fox is just playing catch up. If an American citizen, traceable and with property, does recreational drugs, he risks having a lot of property seized, simply because he's an easy target. If an illegal alien does illegal drugs, no one cares. Why should a Mexican have more rights in the U. S. than in Mexico? Fox is just leveling the field for his citizens.
Come to think about it, why should an illegal alien have more rights (or at least be less subject to the law) than an American citizen?
Is that per NAFTA truck drivers too? What a mess! They can just drive across the border sauced.