No, there is no GPL violation right now. You can reference this FAQ for the reason why.
Yes, GPL does allow public use so no violation here.
Even if the GoFigure author was distributing the binary without source then it still wouldn't be a GPL violation because the gnugo output is not under the GPL and the metamachine interface he is using probably falls under mere aggregation.
Pretty unlikely that one could make mere agregate metamachine. GnuGo output only its chosen move. Not a list of moves or anything. So It is quite difficult (although not impossible) to do a metamachine with just GTP-interface. For instance SlugGo has modified GnuGo engine quite much to in order to do its magic.
Evand: All communication is through GTP, so there is no violation possible. Also, I have not released the code, so again no violation is possible. In the event that I do release it (which I plan to eventually), it will be under the GPL. Releasing it in any other way would seem against the spirit of things, and besides my personal preferences run to releasing things as GPL.