2) The Shadow part of the damage should never miss if the physical part hits.
3) The Shadow part of the damage should never be decreased additionally to the physical damage. It should not "double dip" from resilience et al. Example: My physical portion that hits for 2000 is reduced to 1000. The Shadow part should then hit for 1000 (modulo bonuses) and not 500 or whatever.
4) The Shadow part of the damage will still be increased additionally by talents and anything else that buff Shadow damage. It will "double dip" in the DKs favor. Example: My physical portion hits for 2000 and is reduced to 1000. The Shadow portion hits for 1500 because I have +50% Shadow damage.