I would like to point out that IPMI or Intelligent Platform Management Interface
is an open, industry-standard interface that was designed for the management of server systems over network. It enables you to monitor and control your server platform, as well as to retrieve information about your server platform is a standard. It supports FRU inventory reporting, system monitoring, logging of system events, system recovery (system reset or power off) or alerting.
But what is more important is that all of the aforementioned service processors - iDRAC, iLO or ILOM - are compliant with this standard (or with a specific version of it) so you can either use vendor specific tools to communicate with them or standardized IPMI tools. This may be an advantage when you need to integrate the platform with some monitoring system which supports IPMI standard but not a specific service processor.