When using obj as a proxy in Rhino blocks, Octane creates corresponding materials but when you render, it is just white, although all the textures are assigned in the material. In the preview thumbnail the materials appear to be white as well.
I have attached a screenshot of the materials. Let me know if you would need the files to replicate the bug. The only workaround I came up with is to create those materials manually and replace materials that Octane created automatically, however, after a purge those materials are gone and you would have to import them again.
Octane Rhino plugin version: 188.8.131.52
Rhino: 5 SR14 64-bit