What is ipmi_si and why am I getting a message about it?
ipmi_si is a kernel module that Red Hat and similar decided to discontinue in v6.4.
When doing image changes, Bright Cluster Manager may warn you that this module cannot be loaded, with a message:
Warning: Module ipmi_si does not exist for specified kernel.
This is not something to worry about, because the module is a builtin nowadays in the recent kernels. That is why the message is a warning message, and not an error message. For reasons of backward compatibility, this warning will show by default in the Bright Cluster Manager software for a while yet.
If you don't want to see this warning, then you can simply remove the module from the list of modules used for the initial image and recreate the initrd.
If you are sure that a kernel with a version/release number lower than 2.6.32-358.el6.x86_64 will never be used, then you can safely remove the module.