Since a few days the Certification Matrix for Oracle Fusion Middleware 12c Release 2 (12.2.1.x) was updated within Oracle Technology Network, now Oracle 18c (18.1 on Exadata and 18.3 on On-Premise) is certified and supported as Target Database for RCU (Repository Creation Utility and as Application Datasource.
Certification Matrix for Fusion Middleware 126.96.36.199.0: https://www.oracle.com/technetwork/middleware/fusion-middleware/documentation/fmw-122120-certmatrix-3254735.xlsx. Read the complete article here.
For regular information become a member in the WebLogic Partner Community please visit: http://www.oracle.com/partners/goto/wls-emea ( OPN account required). If you need support with your account please contact the Oracle Partner Business Center.