Reporting back as per the new Masterwork update...simply replacing the old raw folder with the new raw folder hasn't crashed me yet. That was pretty much expected. I also decided to toy with the whole MacNewbie/Masterwork thing, and it seems that replacing the entire Dwarf Fortress folder in MacNewbie with the Mac version of Masterwork's will allow add-spatter to run without crashes (at least, immediate crashes), though at the expense of MacNewbie's ability to automatically start DFHack on launch. I'll look at an earlier version of MacNewbie (I remember you used to have to start DFHack from the utilities menu), but an even easier fix is just starting through MacNewbie>Dwarf Fortress>dfhack. Shockingly, this hasn't crashed me yet, though I did have some unknown world gen issues earlier, where all ores would fail to generate. After re-downloading, the problem
mysteriously vanished. So as of now, my process is:
1. Download newest version of Masterwork (for Windows), Masterwork Mac version (from this thread), Mono's Windows version (if you haven't already), and the 0.7.1 built for MacNewbie.
2. Unzip Masterwork (Windows). Run Settings.exe, which should be possible thanks to Mono. Change settings as you like. Note that not all will actually carry over (only changes to the raws will), but you can at least change difficulty and workshops and such.
3. Unzip Masterwork Mac. Go to "Dwarf Fortress" Replace raws folder with the raws from Masterwork (Windows). Copy entire "Dwarf Fortress" folder.
4. Unzip MacNewbie. Paste in Masterwork Mac "Dwarf Fortress" folder.
5. Run MacNewbie. Toy with settings*
6. Once everything is set up to your liking, go back into MacNewbie>Dwarf Fortress and run "dfhack."
*I have strange errors when playing with tilesets. This was mentioned in the OP, and I wouldn't be confused if it simply crashed on startup. Instead, it seems that you can change the tileset ONCE before the game becomes corrupted. That is, I loaded a fort twice with the default set, and then switched to Phoebus using MacNewbie. Then I loaded twice more, no problems. Then I switched to Obsidian, and got an error (objc[7132]: Object 0x1380faa0 of class __NSCFString autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug). This error is already mentioned in an existing bug report
here. So, if you really hate the default Masterwork set, go ahead and try loading a new one, but backup your saves!
As previously mentioned, I am not so great with computers, so I welcome an easier/more straightforward approach. Also, my testing's been pretty cursory--no guarantees your fort won't become corrupted, though I'm not sure how it *would*, except thanks to the tileset glitch.