Not a VrayLight Mtl, but a Vray mtl which did the same as a Standard Max material with 100% self illumination, that doesn’t illuminate the rest of the scene. It’s not a physically correct material but would be much better to have this rather than using standard max materials for masks.
you can put the vraylight material in a vraymtlwrapper and turn off generate gi, that way it does not create light when used with gi