I downloaded and built munt and when I start it up it listens on port 130:0 and 130:1

export ALSA_OUTPUT_PORTS=128:0
export SDL_AUDIODRIVER=alsa
...
$ mt32d
MT-32 emulator ALSA address is 130:0
Buffer resize: Requested 40 msec got 40 msec / 60 periods
Starting MT-32 core
MT-32 emulator ready

According to pmidi, there isn't anything else listing on these ports:

$ pmidi -l
Port Client name Port name
14:0 Midi Through Midi Through Port-0
130:0 MT-32 Standard
130:1 MT-32 GM Emulation