Got it! Had to re-do both files with the USB Device Filter set, if that makes any sense. It's now showing in Win 8.1 as FRDM-KL25Z. 
Hooray!
I'll have to make a note of this horrible procedure as a last resort for other people in the same boat.
So, now I guess I just put this back in my arcade controller box and plug everything back in... I'm hoping the joysticks in the controller won't mess with the Pinscape. Then VPX will detect it automatically?
VPX just uses the DirectInput joystick interface, so it should see it as long as it's showing up as a USB joystick. You will have to tell VP to enable analog nudge on the X and Y axis, and adjust the gain factor to your liking. I think for VPX the gain factors should be about 10 on each axis - if that doesn't work try 100. For VP9, the gain factor is usually best around 1000.
To see if VP sees it, just create a blank table, run the table, and tilt the KL25Z. You should be able to get the ball rolling by tilting the board.
Hopefully there won't be a conflict with the other joystick. I have heard from one person who was having problems with a two-joystick setup, and I haven't gotten to the bottom of that. If you can't get any effect in VP, let me know and I'll try to help troubleshoot it.
*edit* It seems like I'm getting some unwanted mouse clicks and behavior once I plug it back in.
I'm not sure where that would be coming from - the Pinscape unit is only on the joystick interface, so it shouldn't have any effect on the mouse at all.