Hi, we use a lot of RGB based masks at my studio, so we take advantage of Corona's "CMasking_Mask" element in RGB mode for our objects etc.
Looking at Vantage's documents and forums, they use Vray's "MultiMatteElement" which does the same thing, but it is picked up by Vantage when exporting a render.
Avi responded to me in the forums saying this is currently not supported for Corona and would be a great addition.