This article is fundamentally wrong
Hyper V is a type 1 (bare metal) hypervisor, with cut down Windows derived components (not full fat Windows) on top of it.
Xen, and also Xen server, is a type 1 hypervisor. It uses a paravirtualised OS (designed to be Xen aware) as a domain 0. Dom0 manages access to devices (technically you can run devices off a stub domain, but that's adding complexity), it may also run Qemu which provides emulated devices only - not CPU emulation. The Dom0 can be Linux, NetBSD, or Solaris. For Xenserver, dom0 is a version of Linux.
Why would you use NetBSD as a dom0? Well, Xen is GPL2, but NetBSD is BSD licensed and there's been a fair bit of work performed to create custom embedded NetBSD kernels for specific purposes. Just be aware if you're using PCI passthrough that there's a fair few Linuxisms you'll have to work around, and that passthrough of graphics cards is currently non functional.
There are then DomUs (guest domains) that range from fully hardware virtualised (potentially Xen unaware), to fully paravirtualised (completely Xen aware). The drivers used within these domains can then again either be hardware virtualised, paravirtualised, or in-between (can improve performance).
KVM is a type 2 hypervisor. It runs alongside Linux (and very badly under FreeBSD, with hacks and the Linux compatibility kernel module. Don't bother) as a qemu accelerator. Qemu performs all the instruction translation with optional KVM assistance, it also provides the emulated devices. KVM also comes bundled with vfio on Linux, the most functional PCI passthrough support, particularly in the case of graphics passthrough. These are all separate components. Vfio will work with qemu and without KVM.
FreeBSD has bhyve, its own type 2 hypervisor which works with the FreeBSD kernel. This is quite new, as of FreeBSD 10.0.
Jails are something entirely different.