I looked around briefly, but couldn't find anything - are there any references around about what MIDI values map to in the FluidGM plugins? Do I need to surf the sources?
A little progress - I've been using Polyphone to examine the soundfont files from http://download.linuxaudio.org/musical-instrument-libraries/sf2/fluidr3-splitted/
Things seem to generally match up as far as sending MIDI notes and which samples are played, so that's good. Next I'm going to investigate using sf2utils to try to generate something readable.
I'm not sure exactly what message you are wondering about the mapping of.Program Change messages should just match general midi (hence GM) so something like http://people.virginia.edu/~pdr4h/gmpatch.html
For Control Change messages I'm not sure, but I think all of them map CC1 (modwheel) to vibrato speed.