Initially, there were a lot of problems, but smorovic's fix at the end seems to work (even with XQuartz 2.7.7); so far I haven't hit any problems:
sudo port install wxWidgets-3.0 curl libidn openssl zlib nxcomp libpng jpeg svn2cl cctools libtool autoconf automake pulseaudio
tar xzf nxssh-3.5.0-2.tar.gz cd nxssh CPPFLAGS="-I/opt/local/include -I/opt/local/include/nx" LDFLAGS="-L/opt/local/lib -L/opt/local/lib/nx -lresolv" ./configure --prefix=/opt/local make
sudo cp nxssh /LIbrary/OpenNX/bin/