The problem is not with Octane, its just one of the million problems with fiberfx. If you attempt to move the bones around, you'll notice that the FFX fibers move the hair in the wrong directions. In essence, when fiberfx is applied to an object, in a way the fibers can't actually see the heirarchy as you have it set up now.
I do understand why you didn't attach the hairs to the main model though: FFX has little to no error checking in regards to geometry, so it probably attempted to look at those 4+ point polygons, attempted to turn them into strands, and crashed on you.
With that said, I do have a solution that will work for you:
- Parent the hair guide layer to the cafe_scaler null.
- Set the hair guides object so that it follows the Position and rotation of the character object (in motion options)
- Select any bone on the character object and open up bone properties
- With the bone properties panel still open, select the guide hair object. Within the bone properties panel, you'll notice you can choose to use bones from any object in the scene. Use the character object in this case.
- Press the forward and back keys (move frames) to force fiberfx to refresh your result. This will render properly in Octane.
If you need help let me know, don't spend more time on this kind of issue than you have to