Which part are you referring to?
There is special DAN coverage for any dive professional working as a dive professional (DM or Instructor) in Mexico regardless of nationality.
If you are a US Citizen and here for a vacation or extended vacation or even retired (or not) and living here, but not working as a professional - then you are eligible for standard DAN coverage - I always recommend the Preferred or Master plan - the basic plan is worthless if you really need it because there are so many conditions and exclusions.
Our DAN World contact here on the island is Laura Johnson:
Laura Johnson