Is FCUBS not compatible with PDB or CDB?

Dear Sirs and Experts,

         In our company, we just implemented Oracle database 12c on Exadata. On the Exadata,

there is database which is for FCUBS. At the time of implementation, the implementation team configured database but it is not PDB or CDB.

The reason is FCUBS is not compatible with PDB or CDB and also they said it is best practice for Exadata. So, I am confused.

So, could you tell me "is it correct or not?" It is better if you provides me reference.

Thanks,