Hi,
You can use the H16 hair system right now, as you can see on this post:
viewtopic.php?f=101&t=60507About the new Terrain tools, should be possible use these objects if you convert them to polygonal meshes, as you can see in the attached image. The terrain nodes are Mantra procedural objects, so the only way to use them with Octane is converting the procedural to a mesh object. The shading must be done using the Octane materials, the Mantra materials can't be used with Octane, including all the Terrain shading stuff.
Your best chance to render the Ocean objects is to try to export the ocean elevation data as a sequence of texture maps that later could be used with the Octane displacement maps feature, applied over a flat plane (you have a export to texture feature in the Ocean SOP node). Like happens with the Terrain tools, the shading must be done using the Octane materials. Another faster possibility is to convert the Ocean SOP (used also to preview the mesh in the viewports) to a mesh object, that can be rendered by Octane, as you can see also in the attached image.
Hope this helps,
-Juanjo