It looks like it can be dimmed with a 10V PWM signal. Since the driver can also run on the same voltage, using a 10V power supply might simplify things. Then you'd just need a transistor to convert the arduino's 5V PWM signal into the 10V that the driver needs for dimming. There's lots of examples of how to do that floating around.
EDIT: Oops, I just noticed... Looks like it needs a 200hz pwm signal. You'll need to change the PWM frequency on the arduino or generate the 200hz signal using software. A 20k digital pot is also an option.