So, I'm not sure exactly how they did it, but check out the vDocumentation scripts from arielsanchezmora and Edgar Sanchez. They list this as the RAC IP and it works for HP iLO and Dell iDRAC.
Just grab it from the Powershell gallery, run the get-esxinventory script against your host(s) and you'll get the iLO IP (if configured).
I haven't touched HP in years so I can't help you with setting the IP remotely.
Thanks Ben! Really appreciate you helping promote vDocumentation sir
To the OP - yes, you can use our script and it will get the ILO IP if you are using vsphere 5.5 or 6.0 - 6.5 has an issue that PowerCLI team may fix.
I think that in order for the chassis to administer the blades, they should have an ILO IP, so you shouldn't be in too bad a situation. However, you do need to determine the chassis IP and credentials, and our script won't help you there. To be honest, I would gather the serial numbers and open up a ticket with HP support if you don't know what to do.
To actually setup ilo IP details is not hard, but in a blade environment, the chassis tends to overrule the blades, so it's best to go the chassis route.
let me know if I can help in any other way through twitter, @arielsanchezmor , as I'm not terribly active in these forums
I'm not sure if you're familiar with "Scripting Tools for Windows PowerShell" from HPE. They have cmdlets to interact with the OA and iLO. There is also a cmdlet to find an OA "Find-HPOA", you can select an IP range. I'm somewhat familiar with the cmdlets, and the below link will let you download the module.