I have done a fair amount of residential builds with rammed earth walls in southern Colorado, both Earthbag and slip formed with
tractor bucket and my pneumatic tamper, all in non coded counties. This really begs the deciding factor, which country are they in--and are they within
city limits?
If no codes, then only electrical and plumbing permits/inspectors.
If coded, then they
should have a friendly visit with their permitting department/inspector, and they may need an engineer stamp. They can maybe try to get a permit by offering to build within New Mexico's earthen construction codes (ie post and beam).
What's their soil content?
What's their exterior insulation strategy?