high fidelity animations in fp arms for weapons and such (finger movement etc etc) simpler animations for third person. I am getting a mocap setup soon so i probably wont need the separation of the two but most AAA devs separate them out still due to camera bleeding through parts of the mesh if the animation isnt perfect so its still good practice to remove those parts of the mesh and have the camera sitting just inside the head behind the eyes to give the proper viewpoint. This has been the usual for some time in a lot of fps games its also why in a lot of fps games there is no shadow for the playable character but for immersion reasons i want shadows on mine to suit the game style. Also if ur camera is locked to a bone that is in turn linked to other bones that have mocap movements applied to them the camera becomes really jittery and weird for the player
There is a simple checkbox where you enable the shadows in first person of the third person model, it works well and I use it. So I do not really understand your problem. It is kind of irrelevant of what you use in first person, the shadow will always work.