I posted on the ace Google Group (+rep to Harutyun) and received a reply with the following code:
ace.require("ace/lib/net").loadScript("https://rawgithub.com/ajaxorg/ace-builds/master/src-min-noconflict/keybinding-vim.js",
function() {
e = document.querySelector(".ace_editor.ace-github").env.editor;
e.setKeyboardHandler(ace.require("ace/keyboard/vim").handler);
})
Which works like a charm (Do note that the version of ace that github uses may change, which may break this).
It's a pain to enter this into the console each time, so I plan on adding it to a greasemonkey script (a chrome plugin might be nice! -- well see).
Update
I've written a small Chrome Extension that enables Vim bindings on most sites Ace.js and CodeMirror. Issues and contributions welcome at the github repo