Generally, the CSS part of Bootstrap works exactly the same way with AngularJS as it works with the Bootstrap JavaScript. So as long as you only want to use Bootstrap CSS, you do not have to think about it.
For almost all of the Bootstrap JavaScript functionality, AngularUI provides an alternative approach. E.g. the navbar in general works with CSS only, so just look at the Bootstrap docs and implement it. If you require some responsive features for the navbar, you will require the collapse directive; for an example see here: angular-ui navbar
So if you think anything is missing in AngularUI, could you please be more specific with “are not complete enough to cover the entire Twitter Bootstrap”? I do not have the impression that there is a general gap.
Moreover, http://angular-ui.github.io/bootstrap/ is the most mature library for the task. So if you think there are features missing, I would strongly recommend to patch it and make a pull request.