"You will also need to add the property to the Java command line by adding the following (device names delimited by ":" ) to the file /etc/init.d/openhab in the JAVA_ARGS section with your device names substituted.
-gnu.io.rxtx.SerialPorts=/dev/rfxcomUSB:/dev/zwaveUSB"
I don't know what openhab 'expects' for serial ports, but i suspect it's ttyUSB0. So you would need to add /dev/cuaU0 (or whatever your device enumerates as).
See https://github.com/openhab/openhab/wiki/Hardware-FAQ
Hope that helps,
Paul