Having LSD in the rear will not hurt the VC in the transfer case. The VC is strained when the front and rear wheels are spinning at different speeds. This will happen whether you have 1 rear wheel spinning (in the case of an open diff) or if you have both rear wheels spinning (in the case of LSD). In fact, having LSD in the rear could help keep the VS in better shape, since it makes it harder to spin the rear wheels. All of that is assuming loss of traction. If you are driving in normal conditions, it will make absolutely no difference what type of differential you have in the rear.