Oracle have published an interesting doc 968223.1, entitled “Enterprise Deployment of Oracle BI EE on OC4J and App Servers”.
It details the differences between OC4J and OAS which is useful for the current versions of OBIEE. It then also gives a useful heads-up — that WebLogic becomes the App server of choice in the next version of OBIEE
All of this changes in OBI EE 11g where several projects will become absolutely dependent upon an App Server. Within Oracle Fusion Middleware, WebLogic Server will be the application server and OBI EE 11g will be deployed and certified with WebLogic Server.