OEM utilizes virtual private database (VPD) policies in addition to the standard database privileges and roles. That means that the DBA cannot just give privileges on OEM objects to a DB user, it has to take care of the VPD setting as well.
There are two ways to allow a DB user to access OEM table/views.
The first way is to configure the DB user as an OEM Administrator (Setup->Security->Administrators).Give the DB user/OEM admin at least EM_ALL_VIEWER role and the DB user is ready to access all OEM objects.
The second way is to create a regularly refreshed materialized view in the SYSMAN and grant that view to the DB user who needs the information.
create materialized view "SYSMAN"."UDM_FORCED_LOGGING" tablespace "????????" pctfree 10 initrans 1 maxtrans 255 storage ( initial 64K buffer_pool default) logging using no index refresh complete start with to_date('06-22-2012 14:39:25','MM-dd-yyyy hh24:mi:ss') next sysdate + 1/96
count( member_target_guid ) cnt
sysman.mgmt$group_derived_memberships o ,
sysman.mgmt$target t ,
o.composite_target_name = 'PRODUCTION_SYSTEMS'
and o.member_target_type in ('oracle_database', 'rac_database')
and ( t.target_type ='rac_database'
or (t.target_type ='oracle_database'
and t.type_qualifier3 != 'RACINST'))
and o. member_target_guid = t.target_guid
and t.target_guid = st.target_guid
and st.availability_status = 'Target Up'
and t.target_name not in ('????????')
and not exists
i.target_guid = o.member_target_guid
and metric_name = 'ME$ForcedLogging'
and column_label = 'ForcedLogging'
and metric_column = 'ForcedLogging'
and collection_timestamp > sysdate - 20/1440
and value = 'YES'