According to gulp-ruby-sass (https://github.com/sindresorhus/gulp-ruby-sass) plugin, you need the compass option to be true if you want compass support.
minor compass support fix
We don't intend to support Compass out of the box. But as you've demonstrated, it's easy to enable if you need it.
Alright, but then at the first yeoman question, the add "Sass and compass" answer could be a bit misleading since the gulp adds only sass support, and not compass.