1) - To answer your question, yes, but..... If I remember correctly, a hunt group does not have a specific COS per se. Rather the COS of the first member in the list is applied uniformly to all members, insofar as HG operation is concerned. Again going from aging grey matter, only calls directed to the HG pilot would be affected by this.
That said, I've never used DND for members within a simple hunt group, reserving that instead for ACD or to DND the entire HG. However, I see no reason why it would not work similarly. Ordinarily we would use MakeBusy for this (individual members).
Before making a definitive statement one way or the other I would want to mock it up and try it.
2) Admin (CDE)