The apps probably run in XWayland just like any other X apps. The Window Manager is trickier but apparently XWayland has recently gained support for running a full X root so technically yes:
Huh, that’s pretty neat! But it’s not able to manage Wayland applications, is it? From the Phoronix post it almost sounds like this might be really intended run X desktops on systems that can only use Wayland?
Huh. I was kidding, but I am amazed. 'tis a brave new world indeed.
Wayland has no software other than itself. It's useless.