>> fyi : the upcoming 0.9.6 release of hydrogen adds jack MIDI > and also full jack session support ;)
There you go. So, to the OP, it might be a good idea to use Jack MIDI instead of ALSA. It's easier to learn and use, more portable (FWIW...), and easier to connect to other Jack apps.
For connecting apps that still use "legacy" ALSA MIDI (like pre-0.9.6 hydrogen in this case), there's always a2jmidid (http://home.gna.org/a2jmidid/)