You need to understand that SAS controllers and disk shelves are backwards compatible with SATA disks, but you can't connect SAS disks to a SATA disk cage and backplane (which is what the Gen8 has).
The disk cage and backplane in a Gen8 will not support SAS disks. To use SAS disks with a SAS controller in a HP Gen8 you'd need an external SAS drive tray or similar.
The Gen 8 absolutely supports both standards natively. I have 2, one stuffed with SAS EXOS and the other full of Seagate SATA disks connected to P222s. You can even mix types in the same system but you cannot use cross standard RAID.
HP MicroServer GEN8 - SAS Controller Support
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The Gen 8 absolutely supports both standards natively. I have 2, one stuffed with SAS EXOS and the other full of Seagate SATA disks connected to P222s. You can even mix types in the same system but you cannot use cross standard RAID.