Controlling a hard drive motor with arduino
IIRC hard drive motors operate at 12V, and that board only seems to have one power input, so I'd assume it would be 12V. (I've read that 8-9V is enough, which is reasonable if the motor control electronics drops some voltage)

That might be the voltage across the potentiometer, which may be a problem as the MCP is only rated for a maximum of 5.5V. So if the rest of the circuit expects the potentiometer to vary from 0 to 12V, and you want that range of speed control, then it might not work.

Before doing anything, I'd measure the voltage across the potentiometer's outer pins, when the board is powered from 12V. If that is higher than 5.5V, then you are going to lose some of the speed control range. It's a 50:50 guess, but it may be that you would lose the highest speeds. That may be okay for your purpose.

I assume you have checked that the board can supply enough current for your motor.