Yes, that's ok. The only thing the adapter is missing are the 3.3V wires. The drive can operate with only the 5V (logic board), 12V (drive motor), and Ground wires connected. Very few (if any) drives actually use the 3.3V wires anyway.
The pinout diagram can be found here if you're interested: http://en.wikipedia.org/wiki/Serial_ATA#Power_connectors