No, it does. The 9700 Pro pulls supplemental power from the ADC line just to function even when an ADC monitor is not connected to it. If you try to use a 9700 Pro in a MDD with an appropriately rated ATX power supply that is wired correctly except it lacks the +25V line you won't get any video output.

It's not too surprising. The PC version of the 9700 Pro also needed supplemental power, but that was supplied by a floppy power connector. I would imagine the ATI engineers figured it would just be easier to pull from the ADC line to power the card since the stock MDD power supply had no floppy power connectors.