Type the command TestShowPrivateContent. This will show ‘secret’ Cycles/Raytraced materials. You should add a material of type Cycles VertexColor, and apply that to your object.
Here a quick demo with a vertex-painted Suzanne, exported from Blender.
If this still doesn’t work, could you please share your 3dm with baked skeleton model with me? If you don’t want to share it publicly you can use rhino3d.com/upload to share privately with me. Use nathan@mcneel.com as the recipient.
/Nathan