I inserted midisnoop (from the debian package
https://packages.debian.org/sid/midisnoop) in between the sysexxer output and fluidsynth input and confirmed that the sysexxer is indeed sending my data, but fluidsynth doesn't seem to receive it (nothing dumped when invoked with -d, and no tunings set).
Fluidsynth doesn't dump sysex messages when invoked with -d or --dump, only the "standard" messages like note on/off, pitch bend, prog change etc.
And I think Fluidsynth handles the MTS tuning in a slightly non-standard way... I think the MTS specs say that there is a default tuning for each channel, which you can simply change. But Fluidsynth basically has "no tuning" as default. So when you try to modify tuning bank 0 prog 0, you won't hear an immediate effect. You need to assign a tuning to a channel first, using RPN 03 and 04.
Cheers,
Marcus