Oracle Migration Workbench is for migrating non-oracle database (like sqlserver, access,db2, informix, etc ) to Oracle.

You can downgrade to 7.3 of Oracle.
You can export the Oracle 8 db to an 7.3 home.
You may need to run some scripts to build the appropriate views. Check out the migration guide for 8.0. There's a section regarding downgrading...