Hey everybody,
since there was some confusion with rendering Layer IDs, here is a short howto:
Attribute Editor
Step 1: Make sure your objects geometry type is something different from "Global". So it can be "Scatter", "Movable proxy" or "Reshapable proxy".
OctaneRender Settings
Step 2: Check "Render Layer ID" in the "info passes" tab, to actually render the Render layer IDs.
Step 3: Then select them as a preview pass to display.
Step 4: Finally, make sure Render layers are enabled.
Now all layers are rendered and changing "Active Layer ID" does not change that, like usually.
Result: