Long ago I wrote a post on how to reset the ILO on a HP Proliant server via the command line, as this was often necessary to get a slow responding ILO responding again.
Cisco has included similar functionality in the CIMC CLI, instructions below.
esx01# scope cimc
esx01 /cimc # reboot
This operation will reboot the CIMC.
Continue?[y|N]y
The scope command above allows you to attach to a specific module, so in this instance we are attaching to the CIMC module.
Note: The two links below have quite a good bit of information on the CLI