Yes, sorry. Currently, the LightWave plugin doesn't allow to configure objects lists for the scene update system, so if you enable the update volumetrics option, all the volumes are going to be updated. In any case, the OpenVDB files should be loaded by Octane really fast, but if somehow they need some time to be pre-processed, I'm afraid that there is no solution for this issue currently.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini