olso the same problem
oracle database 12.1.0.1.0
weblogic 12.1.3.0.0 - everything working fine
weblogic 12.2.1.3, with driver ojdbc8.jar, not working

JdbcEnvironmentInitiator - retrieving DatabaseMetaData - in the first case jdbcServices.getExtractedMetaDataSupport().supportsRefCursors() returns false, so Oracle10gDialect.registerResultSetOutParameter is applied (-10 int value)
second case returns true (2012 int value is applied)