Ok, I've found the problem after being stuck on this for the whole of yesterday:
- it was a typo in the module.xml file
I was referencing ojdbc16.jar instead of of ojdbc6.jar.
Once that was corrected, I restarted JBoss AS7 in Eclipse and there were no errors.
I then tested the web service with SoapUI and got back the expected answer from the Oracle DB.
I'm having a similar issue.
Question: What modules directory was you module.xml from?