@hoegaarden_bier I have the same setup (raspberry pi running openhab with a radio). Two of the different methods for getting Raspberry Pi Gateway sensor serial data to Openhab have failed me. One being the perl script mentioned here. Still haven't figured out why it won't work (fully) under a raspberry pi environment. The other option is having openhab read from serial rather than MQTT as mentioned here: http://forum.mysensors.org/topic/655/serial-gateway-connection-to-openhab/32 However, I have noticed that openhab will run the "Item Arduino received update" rule in parrallel when receiving serial messages in short succession. This causes the parrallel rule to overwrite the currently running rules' variable and it becomes a problem. Its also pretty messy and would require you to update your openhab rules on any mysensor updates.
Not to mention, the Serial Gateway you are likely running on your raspberry pi is for opensensor 1.4 (i think) and it going to be completely left in the dust as soon as 2.0 comes around I think.
If you dare, you can follow my project here:
https://github.com/aaron832/Arduino/tree/raspberry-gateway-MQTT (Edit: See Newer Version Below)
Basically I took an updated Raspberry PI serial gateway and updated it to include MQTT.
Just run 'make' under libraries/MySensors and run libraries/MySensors/examples_RPi/PiGatewayMQTT
I am currently looking at getting this stuff onto the develop branch so that it will be around with 2.0