This thread may be of interest. Especially the following excerpt.
Verify OMSA SNMP Settings
If OMSA was installed after SNMP, these changes should have already been made by the OMSA installer. The changes setup OMSA communication with the SNMP agent and give read-only access to the entire MIB tree to the public community. This is required for OMSA and OME to work properly.
1. Open the file for editing:
/etc/snmp/snmpd.conf
2. Verify the following 3 lines exist or add/modify them to the below if they do not:
view all included .1
access notConfigGroup "" any noauth exact all none none
smuxpeer .1.3.6.1.4.1.674.10892.1
You can easily verify that the Dell OpenManage MIBs have been loaded by NET-SNMP running this tool (or whatever your favorite MIB walk tool is) against your Dell server and looking for any OIDs that start with "1.3.6.1.4.1.674"