Spot Hidden is used for when you actively search for hidden objects, traps, secret doors but could also include a living being that has hidden themselves. Scouting is used when you passively can detect things, like when someone is sneaking upon you but also if you actively are scouting out someone, like a group of orcs nearby to determine what they are up to.
A town guard use Scouting if a thief is using Sneaking to sneak by him undetected. If the same town guard suspects that a thief has hidden some stolen goods or even himself in a garden, he use Spot Hidden to find it/him. The thief could also use Scouting to scout out the town guards on a specific street to learn their movements.
Scouting (and some other skills) doesn't have much use in the Riddermound adventure.
Then that brings up the question; If spot hidden is for looking for people that have hidden themselves then that also applies to someone who is sneaking since they have already hidden themselves… that’s why they are sneaking. Why use scouting at all?
If it is a Passive Skill, that brings up another question, how does one determine whether it is a success, does the GameMaster roll against the Players skill level or does the Player roll? If the Players roll, or make a deceleration of intention of that skill, then it no longer becomes passive but active.
It seems that having both skills with no clear distinction between the two (as of now) is an over complication.
Several of my players recommended the following during our run through;
Spot hidden = Inanimate objects (in any situation)
Scouting = Animate objects
Clean, easy and distinct.