I was also thinking about getting a HyperX Predator for my HP Z400 Workstation (same series, single processor machine, same BIOS). Here's what I found out after some research:
according to the manufacturer and some reviews, the drive uses the AHCI protocol and contains an Option ROM which is needed by BIOS based systems to recognize the device.
On Windows, msahci (Microsofts generic storage driver) does the work.
Unfortunately, I could not find out if it's possible use it as system drive.
For my project, installing Windows 7 onto the drive and booting from it was a must.
The chance is 50/50, so I'm waiting to get some more info before placing an order.
In theory, the workstation BIOS should be able to load the Option ROM, to identify the card and to integrate it into the bootable devices list.
Maybe one of the tech guys here (Dan, are you around ???) can give more details about Zx00 Workstation BIOS.
If you plan to use the SSD for data, you're good to go.
Just make sure to not buy a NVMe drive because these are incompatible with legacy BIOS.
Good luck
P.S.: Article HyperX Predator SSD in a HP Z600