The only danger having the spy around would cause is if he somehow noticed that the phylactery Xykon had was not the one he recovered--and the chances of that ever happening is practically zero. In fact, that whole section almost suggests the Giant changed his mind halfway through--for instance, why was Redcloak so sure to make Tsukiko's wights eat her, then themselves, then burn the remnants in the fireplace, only to blurt out that he killed her as soon as he walked into Xykon's presence? Never have understood that.