I worked with BO about 4 years ago. I doubt that the reports are stored on the Oracle server. Here is why:

BO uses universes which are like the end user layer on Oracle Discoverer. They are representations of the data that make it easier for users to design or generate meaningful reports without understanding complicated data structures.

If the reports sit on top of the metalayer, they interact with the db, but may be on a completely different server.

MfG