If you have a need for the Oracle Intelligent Agent, I found that you can run it without any configuration changes. To start the IA try:
$ lsnrctl dbsnmp_start
To stop the IA try:
$ lsnrctl dbsnmp_stop
There do not appear to be any messages indicating a sucessful or otherwise start or stop of the intelligent agent. However, the IA responded to Enterprise manager on the client side so I can only assume that it is working.