Adding to what Andrew replied with is the "process" for discovery... it has been documented by HP in one of the myriad of documents. Here is my condensed and paraphrased version....
Initial Discovery should always begin first with OA’s. Once the discovery task and subsequent identification tasks take place you can review the associations of the discovered devices. Same with the ML/DL iLO’s – with all iLO discoveries you should have a discovered “bare metal” server discovered and associated to it. Since the iLO knows nothing about the OS the discovery is based on the information contained in the System Bios represented by serial number for the hostname. You will also know by icon under HW column whether or not the server is powered on or off at the time of discovery.
For understanding discovery best practice, here's a couple of old blog posts.....
http://worldofinsight.wordpress.com/2011/03/20/discovery-best-practices/
http://worldofinsight.wordpress.com/2011/03/25/discovery-conversation/