Nelson,
There is a big difference in the engineering of the Kingston HyperX Predator M.2 PCIe SSD, an AHCI SSD (nothing to do with ASUS to my knowledge). The controller on the PCB is an AHCI controller.
In the Samsung 950 Pro their approach is an option ROM built into card that supposedly emulates UEFI.... it is not that they have AHCI and AHCI BIOS built into the hardware. Read the section in their white paper here HERE.
Whether that is supported in the xw or the ZX00 generation of workstations is yet to be seen. Maybe it will be wise of you to ensure that you can send things back if the 950 Pro does not work. I have seen no posts where people report getting that M.2 SSD to work in the Z400/Z600/Z800 workstations. You also might want to contact those Aussies at RamCity.com.au for some advice.
There was an earlier Samsung M.2 PCIe SSD that came in two versions, one of which was hardware based AHCI....