My questions:
1. Is there a way to use LimeSurvey in combination with that, and not as a whole page?
2. If not, can I use LimeSurvey just for API endpoints?
1. iFrame (but think about how will look your survey on a mobile device: better to use a full page rendering)
2. Not at the moment (but with LS3 we're getting closer to it, it will probably be available on 3.5 or 4.0)