The defense community term for a while had been Russian led forces. In this war the two 'separatist' army corps are largely operating as an extension of 8th CAA.
Good thread here. A related question, is whether it’s better to call L/DNR authorities/forces “Ru proxies” or “separatists.” IMO both are accurate, $ they still have agency, but as time has passed their autonomy from Moscow was waned so much they they are now clearly proxies.