We have one more question: is there a chance to be wlsdm jar or war file is in the WebLogic classpath.
We are asking that because, the below log generally indicates that issue.

java.sql.SQLException: Failed to start database ‘WLSDM/db’ with class loader PolicyClassLoader ‘weblogic-launcher’ @50d0686 {file:/u01/app/oracle/product/fmw/wlserver/server/lib/weblogic-launcher.jar file:/u01/app/oracle/product/fmw/wlserver/server/lib/pcl2.jar … (642 more)}, see the next exception for details.

If it is not, the reason is may the database corruption you should try the fresh installation.