For further perspective, some started a thread on what to say and do if one has lost valuable time to a high demand group and later, years later, need to re-enter the mainstream society labor force.
Your son should not have to cope with that.
Transitioning from a cult back into society
Instead of working on the dharma farm, there are other worthy and altruistic opportunities he could get involved with that would carry no risk of exploitation and that, unlike Butler's stuff, would look superb on his resume.
Habitat for Humanity.
Service work rebuilding New Orleans.
Join the the groups ?? (Mennonites, Society of Friends/Quakers) clearing up hurricane wreckage on the East Coast.