2D Toolkit will move to a sprite renderer when Unity expose that functionality. For now, the only way to draw anything that isn't just a plain sprite (tiled, clipped, sliced, etc) in Unity 4.3 is using the mesh renderer. You can use unity sprites, or 2D Toolkit sprites in the same scene, but you can't interchange atlases yet. It is our plan to create Unity sprites automatically from a sprite collection when the required functionality is available in Unity.
Basically, we support all the Unity 4.3 function that is available to support right now. A lot of things are internal (e.g. updating a Sprite object) or in some other ways not supported.