There are a ton of reasons to define a different name for Oracle SID and database, however you must ensure that your network configuration is properly setup to support this function. The key is defining the variable GLOBAL_DBNAME in your tnsnames.ora file to match your init parameter db_name, which allows various applications to include EM to resolve the database regardless of names defined.

TNSNAMES.ora for orcl on both SID and DB_NAME.

(SID_LIST =
(SID_DESC =
(SID_NAME = orcl)
(SERVICE_NAME = orcl)
(ORACLE_HOME = C:\oracle\product\11.2.0\dbhome_orcl)
)
)

TNSNAMES.ora for orcl on SID and ORACLE on DB_NAME.

(SID_LIST =
(SID_DESC =
(SID_NAME = orcl)
(SERVICE_NAME = orcl)
(GLOBAL_DBNAME=ORACLE)
(ORACLE_HOME = C:\oracle\product\11.2.0\dbhome_orcl)
)
)

Larry Catt OCP