More progress on this...
hdparm --dco-identify /dev/sda
This will tell if drive can support writing of UNC.

/dev/sda:
DCO Revision: 0x0001
The following features can be selectively disabled via DCO:
Transfer modes:
mdma0 mdma1 mdma2
udma0 udma1 udma2 udma3 udma4 udma5 udma6(?)
Real max sectors: 1465149168
ATA command/feature sets:
SMART self_test error_log security HPA 48_bit
(?): selective_test conveyance_test write_read_verify
(?): WRITE_UNC_EXT
SATA command/feature sets:
(?): NCQ SSP