What if there are guards at the gate demanding ID? Are Bluff, Disguise, and Forgery scouting skills too? And you might have to sneak past guard dogs, so maybe we better add Handle Animal while we're at it. And Open Lock, of course, because you can't scout past a locked door. Oh, and Spellcraft, because knowing about magical threats is important too. Add all Knowledges in order to identify any monsters you spot, maybe some Appraise to tell if the treasure is valuable...etc. Pretty soon you need every skill to be a scout.