You can get this information via IPMI via iLO for most ProLiants but I think that iLO itself only provides SNMP information about itself (interface stats, power state, ip-address, link speed etc) and not detailed data such as power draw\temps\fan speeds from the SM\PM bus. All references that I can find require that the OS is running and a software management agent is installed.
Nagios supports IPMI though AFAIK so you can get it that way provided the server allows it - if I remember correctly the low end 1xx series ProLiants do not provide this level of out of band management (there is a similar restriction on Dell's 1xx Series too just in case you are checking them out).