It was somewhat difficult to install on Centos (mostly just getting a Sun JVM installed sanely) until they added the yum repository. It is still somewhat complicated to deal with all of the things it can do so I'd suggest joining the mailing list if you haven't already. It does support many more devices out of the box than netdisco, including hosts as well as network equipment. If you want it to collect snmp data for graphs on the switch ports that don't have addresses you can set collection manually for each one or just change snmpStorageFlag to "all' in datacollection-config.xml.
OpenNMS is now crawling my network and discovering all the servers. I'm not seeing how to find which switch and port each device is plugged into. If I browse to a node and click on it's network interface, it says this:
-------------------------- Link Node/Interface No link information has been collected for this interface. --------------------------
Is that where the port and switch information is supposed to show up? Or am I looking in the wrong place?