I would like to do a Shadow Catching Ground in VRay For Maya using the VrayMtlWrapper shader, a bit like the way it's done with Mental Ray and the mip_matteshadow shader. I have something close but there is an issue : The ground is not letting the Environment Lighting passing through. I have pretty much the same issue with 3dsMax :
Here is a render with no ground :
and the same with the shading network :
The second render is missing all the bottom lighting from the Environment File, only receiving the ligthing emitted by the base shader of the VrayMtlWrapper.
Notice the is also kind of an alpha compositing issue.