I think you are talking about loss of tail rotor effectiveness LTE ( or fenestron stall ) not Vortex ring state .
AFAIK VRS is only normally talked about in relation to the main rotor. To get VRS in a tail rotor you would be moving the rotor through its own wake and as such would it not be a self correcting phenomena ( get into wake lose thrust rotate out of wake regain thrust ) ? There have been many discussions on here in the past about LTE and Fenestron stall from people much wiser than me.