MDK does run well on my primary test Mac (GMA 950 MacBook, CXG 10.3, 10.6.8) with some caveats:
a) The 3Dfx Glide wrapper that's worked best for me is nGlide.
b) To get the GOG release to work with nGlide, I needed to use alternative EXEs for the game that had special alterations (see http://www.codeweavers.com/support/wiki/dmca ).
c) The game is apparently hard coded to run at 640 x 480. The nGlide configurator utility does help in getting the game to run forced on a stretched resolution, which does help somewhat.
Other than these issues, the game runs well.