SATA doesn't use the SCSI command set. It's all still ATA, right down to the inability to abort tasks. (But it is common for operating systems, such as FreeBSD, to model all commands internally as SCSI commands and just translate them to ATA commands if necessary at the last minute.)

SAS HBAs are backwards compatible with SATA drives because they're specifically designed to be. So I guess they're capable of passing either SCSI or, when SATA drives are used, ATA commands.

Where it gets amusing is when you use SAS expanders, since then the link from the HBA to the expander is SAS, but the link from the expander to the drive is SATA. Thus SAS has a special protocol called Serial ATA Tunneling Protocol (STP), which allows ATA to be tunneled over SAS.

What's really comical is that this means if you attached a SATA optical drive to a SAS expander, it follows that you'd be talking SCSI tunneled inside ATA/ATAPI tunneled inside STP over SAS.