Oracle has some goofy licensing when it comes to virtual servers, they essentially license off the physical hardware that the server is on and not the virtual hardware assigned to the Oracle VM.
IBM/Oracle licensing with virtual servers - http://www.vmware.com/community/thread.jspa?threadID=94868
There have been a few posts on people running Oracle...
http://www.vmware.com/community/thread.jspa?messageID=703431򫯇
http://www.vmware.com/community/thread.jspa?messageID=711348򭪴