I searched on the documents and through the forums and haven't found a definitive way to import WHM/CPanel backups. There is a 3rd party plug-in marked as beta and leaves some key things out on import. I would highly recommend including the following answer in your formal documentation and include this capability into your product. This is the only thing keeping me from moving over and I'm sure there are MANY others in the same boat.
What is the definitive way to import WHM/CPanel backups to VestaCP?