BlueOnyx now includes an API for remote provisioning of Vsites and Users, for suspending or deleting Vsites, for password changes and status checks. It was designed especially with WHMCS in mind.
WHMCS module to manage BlueOnyx servers is available free of charge here. Please note there are two modules: One for BlueOnyx 5100R (covers 5106R, 5107R and 5108R) and one for BlueOnyx 5200R (which covers BlueOnyx 5207R, 5208R and 5209R). For more info please see the API Documentation.