Hmm, sorry, but I can't find any problem in this scene. If I add a null including the Octane volumetrics, the OpenVDB sequence is loaded without problems. Are you sure that you don't have a problem with the OpenVDB files paths in your scene? Perhaps the relative path is not working or something like that. In the Octane log file you should get a message about what file is trying to load the plugin, and perhaps a warning about a not found file ... something like " - Volume object from the OpenVDB file xxxxxxxxxxxxxxxxxxxx"
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini