Oracle Business Intelligence needs dev_platform and dev_mds schemas which are created by the rcu tool (Repository Creation Utility). RCU also creates a temporary table space.
During performance testing I was monitoring the space taken by the schemas and the temp tables space and they did not change. Therefore it does not matter where the repository schemas are installed. I generally install OBIEE on a powerful machine at least 4GB of ram. I create the repository schemas on a database on separate machine which does not need to be powerful.
