Not really a help request per se as I just figured out my own problem, but I'm leaving the solution here for posterity. I have already submitted a bug report with similar information to that below.

The ImageMagick programs contained within the BXH/XCEDE tools don't appear to work on current versions of Mac OS X (I'm on El Capitan here, but from my searches it appears that this bug would happen for any version >= 10.7 Lion). I ran into this using fmriqa_generate.pl but any other functions that use ImageMagick likely have the same problem.

Errors like this appear when invoking ImageMagick's 'convert' or 'montage' tools:
dyld: Library not loaded: /System/Library/Frameworks/OpenCL.framework/Versions/A/Libraries/libclparser.dylib
Referenced from: /Users/mjohnson113/Downloads/bxh_xcede_tools-1.11.1-MacOSX.i686/bin/convert
Reason: image not found

From web searches, I deduced that the .dylib in question doesn't seem to exist anymore in Lion and up.

I fixed the problem for myself by installing ImageMagick via MacPorts and replacing the 'montage' and 'convert' binaries in the BXH/XCEDE package with the freshly built copies from MacPorts. Not sure what the best long-term solution would be for the project.

Anyway, if you are having the same problem, installing your own copy of ImageMagick and replacing the broken BXH/XCEDE copies with custom-built ones should, in theory, work for you too!