We.ve been running Genesys 5.1.5 on Oracle 8i (8.1.7) for some time with no problems. Drivers we were using previously (7.3.4) were compatible so changed very little apart from DB upgrade.
We upgraded a development copy of the database first, pointed Genesys to it, and tested end to end. Everything ran from a Genesys point of view, however, we only run the outbound suite although I doubt whether that would make too much of a difference.
We then backed up the production DB and migrated it. Testing end to end again showed no problems so that was that.