I'd like to turn my Linux Mint desktop into Xen host. Will I be able to use VirtualBox inside Dom0, just like without Xen? What the limitations would be (if any)?I believe, that this might not be possible, since both VirtualBox and Xen utilizes CPU rings, and they might fall into conflict.Note, that I need to run VirtualBox under Dom0, not DomU. 
Can VirtualBox run under Xen Dom0?
virtualbox;xen
According to this thread, titled: VirtualBox Running on top of XEN kernel, possible? it sounds like the answer is no it isn't possible.