Brendin,
When you get around to adding the keypad, open up "Keygrabber" (happy face icon) in the Mach 3 folder on your C: drive as Hood suggested.
I would think if it was going to work, it would show up under the "HID controllers" tab or possibly the other tabs since it's actually a keypad.
I won't be much more help as I've only used a game controller through KeyGrabber.
Dave