Can you visualize multiple materials using MIB rendering?
unfortunately not at the moment. From release R2019a, Matlab has labelvolshow function that suppose to do that, but it is missing lights and shadows, which makes it quite useless. When/if they fix that, I include it to MIB rendering.
Currently, the only way to show multiple materials of the model inside MIB is to use Menu->Models->Render model->Matlab isosurface
In this mode, MIB calculates surface for each material and show all those surfaces together over a selected slice as shown here: