Can Discoverer 11g reports be migrated to OBIEE 12c without migrating to 11g?
This is for a fresh OBIEE installation.
It isn't possible 'cause OBIEE 12c doesn't have ORACLE DISCOVERER METADATA CONVERSION ASSISTANT
To achieve that you should:
1 - Migrate Discoverer 10g (10.1.2.x or +)/11g to OBIEE 188.8.131.52.X or + first;
Article: Migrating Oracle Discoverer Data to Oracle Business Intelligence 11g
2 - So you could migrate OBIEE 11g to 12c;
See that too