vim-athena doesn't depend on or use any version of GTK+. If you use sudo apt-get build-dep vim-athena, it probably will install GTK+ and GNOME related libraries, because the vim-athena binary package is built from the same source package as vim and other vim-providing packages. In any case, you shouldn't need to build from source, as the binaries provided by vim-athena are already built against Athena and not against GTK+ or other graphical toolkits.

Fortunately, vim officially supports some GUI's other than GTK+ and Qt, and one such build is officially packaged for Ubuntu. Just install the Athena version of vim, which is provided by the vim-athena package.

vim-athena

/usr/bin/vim.athena --servername local