• PxrVolume is a Bxdf and should be used in the Material Connection of any Shading Group (SG) node. Connections to the Volume connection are not correct for RenderMan.
• The OpenVDB node defaults to having its indirect visibility set to "off", this is because Maya's old defaults have imported objects as invisible to reflections/refractions in the Render Stats rollout of the attribute editor. Turn these on for correct rendering.

The Maya Cloud Pattern/Texture will not operate as expected in PxrVolume because of how it calculates the falloff effect.