Do you mean that I will have to use the Standalone version to create a material containing the VDB then save as ORBX?
Yes, you need to create and edit the ORBX file in Octane Standalone.
I always wonder why some features of Octane are not implemented in the Rhino version, is it just not possible?
Rhino doesn't support VDB files, so adding support for them in the plugin does not really apply. It is easier to use ORBX proxies. At some point in the future I will make it possible to edit the ORBX from within the Rhino plugin.
Thanks
Paul