Receiving shadows yes, ambient will come as soon as Alic gets to it 🙂
As far as we can tell everything is still compatible with Unity 5 so its just a matter of time heh. There are a few complexities that make it not possible to merge it into the main Spine-Unity runtime at the moment, but the plan is to put a forked SkeletonRenderer up that people can import and make use of if advanced shaders are needed. Obviously said shaders are really expensive compared to the normal Skeleton shader.