Elza has been known to "help" Rand, too, not because she wasn't a Darkfriend, but because she believed it served her purposes as one to do so. It would be kind of a giveaway if every single Darkfriend was constantly screwing the Light and its servants at every opportunity. Sheriam helped Egwene a great deal when it suited her, not because she was playing mole like Verin, but because she was playing her own (BA) game.

As to the other, I believe someone had to know where the adam was, and that "somewhere in Caddys quaters (unless she stashed it elsewhere)" wasn't good enough unless they ripped the place apart finding the adam, which there's no reason to think they did and some reason to think they didn't.