Unfortunately, the Octane core doesn't support attributes yet, but the good news is that this is a planned feature for Octane 4. Once available in the core, I'll add all the attributes related stuff to the plugin ASAP.
Meanwhile, the plugin has some workarounds to support at least the color attributes for the particles, hair and instances, something that can help in a lot of projects.
I hope to have good news about this feature really soon!
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini