Hello Calum,
Yes you need agents on your operating systems, these can be downloaded from the hp website. The agents are available for windows, esx and many linux platforms. When these agents are installed you need to set credentials for discovery in SIM like signin, snmp and wbem.
Ilos and enclosures don't need credentials. If you need more help let me know how far you got it working then we'll start from there.
Kind regards,
Andrew