Yes, you need the right privileges. https://github.com/openhab/openhab/wiki/GPIO-Binding#installation
You could switch to root once as proof of concept.
Regarding the gpio group: I’m not sure why it is not there and how you could use it. Would you consider trying to create one and then working through this: http://raspberrypi.stackexchange.com/questions/40105/access-gpio-pins-without-root-no-access-to-dev-mem-try-running-as-root
