Currently, for disks Mach integrates drivers from Linux 2.0 through some driver glue code. As it's very old, that limits hardware support a lot, of course. For network boards, we use the DDE toolkit to run linux 2.6.32 drivers in userland processes, which provides both long-term support for new hardware and safety against driver bugs. Firmware loading is however not implemented yet. Xen is also supported, both blkfront and netfront.
Note however that we have of course not tested all drivers, we obviously don't even have all kinds of hardware. So we can not promise that they will all work. What probably works for sure is what we usually use: the rtl8139 or e1000 drivers for instance.