Update:
SSBM is playable, more or less.
The Joystick on the arcade stick is by default mapped to the d-pad, but there is a mode button that allows it to function as the analog joystick (only with digital input) and also as a C-stick.
I'm not sure I like it as well this way, but I need to spend more time with it to see for sure.
FWIW, the joystick makes the Midway Arcade Gallery worthwhile, and it makes Mortal Kombat a lot more fun.
I'm definately ordering Capcom vs. SNK, and I'm also looking for Soul Calibur 2 at a decent price.
The Joystick was a great investment, I can't believe Gamestop had it so cheap (only $29.99).