Is Conqueror's Haki Indiscriminate?
No, it isn't indiscriminate. 

It can be used by the user selectively.

As stated in the Wikia:


  This type of Haki grants the user the ability to dominate the wills of others. The most common usage of it shown in the series so far is using it exert the user's willpower onto those with weak wills and rendering them unconscious. Whilst inexperienced users are restricted to merely overpowering the will of one individual or blindly knocking out weak-willed people around them, those with more expertise can pick out weak-willed individuals in a large group and knock them out without affecting the others.


An instance of this is shown when Camie isn't knocked out when Rayleigh uses it for the first time.