Multimatte from Shader Material ID and Shading Groups

V-Ray V-Ray for Maya Issues
1

Is it possible to generate two different Multimattes from Shader Material IDs and Shading Groups? The Material ID of the Shading Group seems to overwrite the ones of the shaders.

2

This is not possible currently - the MultiMatte from the Shading Group will always overwrites the ones bellow.
You can use other render elements for additional masks like Material Select / Material ID / Object ID / Render ID and etc