Fact is, there’s always been employment void in the USA filled by ‘voids’. Really, this kind of situation is (nearly a) (classical) libertarian paradise in a sense: Yes, they have to fly under the radar and keep their noses clean.
But as long as they sign no papers, ask for nothing from the government, do nothing on paper, don’t go to hospitals or police or prison, are entirely invisible to the system in every which way, well, there ya go.