Oracle is supported by professional version but as is community can not be used. I will try to explain, there's some code optimizations to get Oracle running what are not present in community. If you want getting community version with Oracle must configure Oracle dialect as is described here
http://wiki.openkm.com/index.php/Using_ ... _databases and then make some improvements in source code ( here is developer guide if you want working on it
http://wiki.openkm.com/index.php/Developer_Guide ). I advice in advanced that us only we will maintaining Oracle for professional version ( there's a lot of work on it ) and if nobody want to support it on community version we will not doing maintenance on it ourself. I want to be clear about this point. We'll be please if someone wants doing it, any help, contribution from community users is always wellcome.