The install is essentially the same, also depends on if you're going to set it up from the GUI or command line. But, you get a livecd ISO, set up your harddrive space through Xen, boot up the livecd, partition it up (i.e /boot swap /), get the Funtoo stage3, install the system, set root password, reboot, remove livecd ISO, start it up.
I ran Xen on my home server for Funtoo VMs for a few years until I switched to KVM. I don't really remember anything specifically weird about installing on Xen. Kernel config was made from looking at lspci, lscpu, etc. I think the only thing that I specifically remember being a little weird was the harddrive was called
So, really it's just as simple as installing to bare metal.