According to the Oracle documentation Enterprise User Security (EUS) works with Oracle Enterprise Manager Grid Control. The steps in the documentation: http://download.oracle.com/docs/cd/B16240_01/doc/em.102/e10954/security2.htm#i1036425.
The steps explained there are easy to follow and correct. The repository of the Grid Control (GC) is setup for EUS and works fine. But just for sqlplus sessions to the repository and one would want to login to the Grid Control console. That unfortunately didn't work. The authentication went ago, but the user didn't have the propers authorization. But even giving the EUS user the proper GC authorization didn't make it work:
SQL> grant MGMT_USER to EMGC_EUS;
Login still din't work, see the picture.
The work around waqs to create a regular GC user thru the GC administration console. Then drop this user from the GC repository. That means the database user droppped, but the GC user is still defined. Then the EUS user can login to the GC console.