The HP Z8 G4 does support NVMe RAID on Windows boot drives using the Intel VROC upgrade.
What you need HP Z8 Workstation At least 2 matching NVMe SSDs on the internal HP NVMe card slot. Part #933576-001 The Intel Premium VROC SKU#VROCPREMMOD Create a Windows 10 Restore flash drive using the HP Cloud Recovery Client tool. hp.com How to enable Install the VROC in the plug just below slot #7 near the bottom rear of the motherboard.
Read more →