I use HATARI-v1.3.1 on my MacMini with OSX 10.7.2 and a Bluetouth Keyboard. I have the TOS 2.06 (German version). The following description refers to this combination, but may also be useful for different ones.
The keypad mapping follows mostly the signs. Y and Z are correct. Some keys at the right edge are wrong: ß, ü, +, # . The key </> (smaller/ greater) at left lower corner its not used in HATARI, but I found a way.
The file "keymap_thuth.txt" from Thomas Schaerer I didn´t need. Anyway, it was the base for my file. I have to mention that Thomas was very helpful with every question! I set up a new file (i.e. MacHatTast.txt) with just the following lines (only a little bit different from JonB):
#45 is the ASCII-Code for - (minus), 12 is the code for ß-key on ATARI-keypad
45,12 # SDLK_MINUS = 45, ß and ?
91,26 # SDLK_LEFTBRACKET = 91, ü
92,41 # SDLK_BACKSLASH = 92, # and ^
93,27 # SDLK_RIGHTBRACKET = 93, + and *
96,96 # SDLK_BACKQUOTE = 96, < and >
This file must be selected through HATARI menu under "preferences...(keyboard)" by "choose" and than saved. That is (as I found) necessary for any alteration to this file. Than "ok" and "cold reset" through menu/emulator. That´s it.
The left upper key ( ^ and ° ) I left as it is. The caret-sign is the upper case of # like on ATARI, the degree-sign I couldn´t localize on the ATARI-keypad.
After I had lost several times all my settings without knowing why, I found at a time, that the hidden file .hatari/hatari.cfg, where all the preferences are stored, not allways was saved accordimng to the alterations. If the keyboard doesn´t work the intended way it´s a good idea to check this file.