As privateers? Letter of marquis?
Pretty sure they are soldiers of fortune, but I cannot be right all the time...
It was set up to be a deniable army following orders coming from Putin and not an independent profit-seeking enterprise. It also acted as a place to put the military men, who got other than honorably discharged. A second chance unit, that doesn’t let the training state spent money on go to waste.
This rebellion is not very different from a rebellion by a regular army.