Hi:
To be able to develope a WHMCS addon, your dedicated server provider( or software) must provide an API( https://en.wikipedia.org/wiki/Application_programming_interface ) or access to IPMI command line tools to receive commands from your WHMCS instance. If your IPMI interface can only be managed using the built in IPMI panel, i'm afraid that is not possible to develope the addon.
Best regards