The default snmp configuration is not very usable, that's why I change it.

First of all, I create a view (named All for example) which grant to see most of avaiable MIB. Then, I add - at least one - community line to allow my snmp manager to query AIX.

/etc/snmpd.conf

community       public   192.168.1.0 255.255.255.192  readOnly All
view            All             iso.3 system enterprises view internet host

The host part in the view allow to query the HOST-RESOURCES MIB, which include values like storage, CPU utilization, etc.. If you want this one, check for hostmibd is running.

Note: I notice that AIX 5.1 and 5.2 have a bug regarding the CPU utilization, just look :

% snmpwalk -v1 -c public 192.168.1.48 .1.3.6.1.2.1.25.3.3.1.2
HOST-RESOURCES-MIB::hrProcessorLoad.1 = INTEGER: -2147483648
HOST-RESOURCES-MIB::hrProcessorLoad.2 = INTEGER: -2147483648

If you have the same value, you need to upgrade.