A couple years ago I bought a Logitech gamepad that happened to use Xbox protocol (I didn't read the label well enough, I just saw the name brand). I tried to use this Xbox360Controller driver but it didn't recognize my gamepad. So, I fixed the driver to work.
When Mountain Lion came out I had to update the driver, which had undergone some 32bit -> 64bit change but also added in some other garbage about Xbox chat pads that was breaking when I tried to use it with my Logitech game pad. I don't remember if it kernel panicked or just didn't work. Certainly I caused a kernel panic or two while tinkering with the driver. But I got it working again, mostly by commenting out stuff I didn't want.
I have kernel panic with this driver unfortunately. Wired XBox 360 with iMac 2011 and MacBook Pro 2012. Not sure what caused the issue... Because of it, I installed Windows via BootCamp and play all games over there, a bit inconvenient.
Which version of Xbox360Controller and what Mac OS version? You might want to try an older pre-64bit version of the driver if that will work on your OS.
Or you could try to debug the source if you're up for that. I would try but don't have the expertise to help without seeing it and tinkering with it.
I have never faced any issue using the controller to play steam games on my mac.