Oracle 18c should be supported by OBM Management Pack for Oracle Database.
We have multiple instances in production with version 18.x and looking for MP release ASAP for the 18.x version. We are having hard time to get the supported version released for new versions OS/DB. We had to do months of followup to get MSSQL 2016, Solaris 11.4 Agent support (still not official supported).We would expect MF to release relevant fixes in time.
Please let us know when its going to be released.