I have a rather simple question:
I want to run openHAB on an raspberry pi and - Is it possible ( also recomendable) also to run a script to integrate sensor data (e.g. dht22 temperature) on the same raspberry?
There is no problem with that setup. If you choose to not use the GPIO binding that is a perfectly acceptable arrangement. So long as the script doesn’t use so many resources that it starves OH, which is unlikely. Also, any ports the script uses and OH uses must be unique (e.g. you can’t have your script use port 8080 because OH uses that networking port).