The optional HP Microserver Remote Management Card (BMC/RAC, call it what you will) features IPMI, which I previously had configured using OpenIPMI on my Centos 6.3 system. There was one issue that required working around, in that the BMC address as reported by the BIOS was 0xCA8 rather than the real address of 0xCA2. To get the ipmi module to load you had to create the file:
options ipmi_si type=kcs ports=0xca2
That all worked nicely until I upgraded the server to Centos 6.4, at which point IPMI stopped working completely. What has happened is that RHEL now has the ipmi driver built into kernel and not as a loadable module any more (who's bright idea?).
You can read all about the driver here.
The fix is now to pass the driver options to the kernel at boot by appeneding the cmdline for the kernel in GRUB with: