See Lines 539-543 in ace demo.
Basically you need to load emmet source script (e.g. from https://github.com/nightwing/emmet-core/blob/master/emmet.js) and ace extension from /src/ext-emmet.js
call require("ace/ext/emmet");
so that requirejs executes the script
And after that call editor.setOption("enableEmmet", true);
.
See jsbin.com/ace-emmet/1/edit for live demo.