The chassis OA has the ability to over-ride existing iLO configurations and talk to the blades no matter what the previous admin did. You should be able to apply iLO configuration values to the iLO via the OA. If the OA can't talk to the iLOs on the blades, you have a problem.
One of my customers has a couple of C3000 chassis. With an older firmware, the iLO on the blades would become non-responsive both to the chassis and to the rest of the network (the iLOs were IP-enabled for IP-KVM purposes). This was repeatable, and all blade iLOs would go unresponsive within about an hour of each other, 30 to 90 days after being started.
The only way to get everything talking together again was to power-cycle the whole chassis -- shutdown all blades, then pull the power inputs. Removing and reseating individual modules didn't work. I will admit we didn't try the downloadable iLO configuration application; a couple of these blades run ESX, which makes the tool rather academic anyways...
In our case, HP denied there was a known problem even though both of our chassis exhibited the issue.
Depending on when this chassis was shipped, you may be in this boat. Look for, or call HP and ask for, a firmware update and apply that. Note that you have to update the firmware for all components -- OA, VC (if you have it), as well as individual iLOs, and blade BIOSs. The whole chassis will be inoperable during this update, and components are updated serially so it can take several hours to run. One co-worker told me that he'd been warned by HP that there is a specific order you have to run the updates in, otherwise you risk bricking components; however an HP service agent denied that. In the end we managed to get HP to deal with it as a warranty issue, we raised enough of a fuss that they had someone come in and do it for us.