Octane doesn't support any kind of interpolation for the curves rendering. They are always rendered as straight lines between the control points, so if you need to smooth the hair curves you are going to need to add more points to the curves, probably at the SOP level, because the "Display as subdivision curves" only affects the viewports but not the underlying data retrieved by the Octane plugin.
Hope it helps,
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini