I don't have a Mac, but I presume you're having trouble because the Launcher isn't cooperating with you.
What you could do is simply extract the KeeperFX archive somewhere, and copy the correct files from the GOG version of the game into that. You can find which files that are right here.
Then run the game with wine, and possibly with the correct command line options to force windib instead of directx (see command line option -viddriver).
If this doesn't work, please share exactly where you are having problems.