Seems like nobody replies to messages in 'General', so I'm reposting here...
After popping open the microbrute and seeing how signals are routed, it's clear that there is no technical reason that the synth wouldn't be able to respond to note velocity.
Both the LFO and Cutoff CV for Mod Wheel control are generated by the MCU, independent of one another. When the Mod wheel is set to 'LFO depth', the +/- 5V LFO generated by the MCU is attenuated, and the cutoff control signal is always 0V. When the Mod Wheel is set to 'Cutoff', the LFO is transmitted at the full +/-5V, and the 0-10V Cutoff signal is generated.
Since the microbrute's keyboard generates velocity, if the firmware were updated, velocity could be routed to the Mod Wheel destination that isn't being used by the Mod Wheel. Velocity depth could be controlled by external MIDI or from the software interface.
Note that this is different from the 'velocity hack' of routing velocity back in as mod wheel data in that the synth would be able to respond to both mod wheel AND velocity simultaneously.