I’m not an expert, but from what I understand, the answer is “no”: Xen is what runs on bare metal (it’s a Type 1 bare-metal hypervisor), and dom0 is a VM (it’s the zeroth Xen domain).
This is exactly right: somewhat simplified:
In Type 1:
Hardware → hypervisor → dom0, domU…
In Type 2:
Hardware → OS → hypervisor → VMs
dom0 is the initial VM started by the hypervisor - it is the first
domain to be started, has privileged access to hardware, provides virtual
disks to the domU,and runs the Xen management tools.
I thought about that too but IIUC Qubes OS uses a modified (not “vanilla”) Xen, so I suppose it is more relevant to ask here and have the answer available to the whole community.
I am confident there are highly qualified people here, so hopefully someone can step in and shed some light on the matter.