You won't find any features from other CAD systems when opening models in Creo, because it's (I think) almost impossible to translate such data between very different underlying systems which use different algorithms and methods for building geometry. So the Unite technology still "imports" just the geometry and it will not transfer features, you get geometry and Flexible Modeling tools (aka direct modeling) to make changes.
As far as I know, Unite is supposed to eliminate (or at least reduce) the need for intermediate formats, like STEP or IGES - the user is supposed to simply pick the model from supplier, put it in his assembly (without converting it to Creo models) and use it as references for placing other models or features. What's more, when said model gets changed by the supplier, user can replace the model on disk with newer version and Creo will pick up the differences and will show where the geometry has changed. Also, when the modification is needed, Creo converts foreign model "on the fly" to Creo model and allows editing with Flexible Modeling (saving changes to dummy file, so the can be re-applied when original model from other CAD changes).
So that's the point of Unite technology - to reduce time needed for incorporating foreign models and convert models on "what needed when needed" basis.
I can't speak for the collaboration features and exporting models to different CADs, since I haven't worked with that.
