How can I power a SCSI hard drive without a motherboard/scsi card?
This connector is called Single Connector Attachment (SCA): Wikipedia page. This should help you find a pinout.

Also, AFAIK, ALL disk drives require the controller electronics to be powered to spin up a drive. Powering the motor alone will not spin up the drive. Also, I wouldn't guarantee that if powered but with no host communications, the controller wouldn't eventually spin gown the drive.