I'm an active Cyberboard module designer but have not (yet) gotten too active with VASSAL. I'm also a teacher and have used and enjoyed this game by Garry Spence. I recently contacted him to obtain go ahead for my using his graphics in a CB module and he has agreed to this.
From my emails with him I don't get the impression he is familiar with the range of online/PBEM gaming options or aware of your VASSAL module using his game graphics.
If you haven't done so I think it would be a courtesy to approach him about making the VASSAL module available publicly. Even for a free game it seems fair to do so. I'm sure he would agree.