III percenters and white supremacists organizations -along with gang and cartel organizations - have been sending their younger siblings and children to the Army and Marines for decades. Wealthier organizations even get some members into the Service Academies. And the DoD knows it.

They do this primarily to teach their younger members the latest and greatest in weapons and tactics in a legitimate setting rather than haphazardly in "secret" places where the police or FBI might interrupt, and also so those younger members aren't a drain on their resources.

The only risk these paramilitary or criminal civilian groups run is that the young member might have a change of heart and leave those ignorant angry he-man clubs behind. Which does happen to at least half, from what I've observed. Something about getting out of the bubble and learning about the real world can do that to those who are basically decent people who were raised by angry idiots with agendas.
And as the military is one of the largest socialist organizations in the world, a person raised in a militia or criminal setting can quit that "family" fairly easily; stay in, do their 20 or 30 years, and retire comfortably far away from that former upbringing. I have observed this in person over the years.

Haele