Angular uses DOM templating instead of string-based templating (most current JS templating engines are string-based), so you would definitely need to fire up a headless browser (PhantomJS) or DOM (JSDOM) of some sort to get it working.
It would be very slow if you were doing this dynamically so you would probably want to regularly compile and cache your pages.
Yeah this is the best way to serve rendered pages to search engines. I also found this project: https://github.com/ithkuil/angular-on-server - Which might be worth looking at too.
The first thing I thought of that is similar to Rendr is http://meteor.com/ . I'm not sure about how it works with Angular. It does describe itself as a framework where Rendr describes itself as a library, so I'd think it'd be easier to run Angular stuff on top of Rendr.
There's also hoodie + yeoman, but there aren't any adapters for angular yet. For some reason angular doesn't get official love from libraries like rendr and meteor.
