According to that link you posted:-
This DFRduino Arduino motor drive shield allows an Arduino Duemilanove or Arduino Mega to drive two channel 7-12V DC motors. It uses a L293B chip which deliveries the output current up to 1A.
So why are you asking the question?
However the link is very poor on details but it sounds like it uses the Vin voltage to power the motor. That is the voltage you get when powering it from an external power supply through the jack.