Hi,

Oracle publish XLS files called "Certification Matrix" where you find the official supported environments (OS, DB etc.) for OBIA, OBIEE, FMW etc.

The one you look for can be found on this page and the direct link is: http://www.oracle.com/technetwork/middleware/bi/documentation/biapps-11-1-1-10-1-2706781.xlsx

So yes Oracle DB 12c is officially certified, but it's better if you have a look by yourself to make sure you have the right combination of OS - DB etc.