I disagree. I don't think you can choose not to spot an orc. If there is an orc in play, you have to spot it, can't just close your eyes and say: "I see no orcs? Do you?".
This excerpt from the rulebook is how I defend the position that you are only forced to spot something in play if the wording is "you can spot":
Normally, you don't have to spot all the cards in play that meet the requirement if you don't want to.
If a card says, "for each Elf you spot" and there are 2 Elves in play (and active), you may choose to spot 2 Elves, 1 Elf, or none.
However, if a card says, "you can spot," that means you don't have a choice and you have to spot anything and everything that meets the requirement.
"While you can spot The Balrog, skip the archery phase" means you can't make a choice (it either works or it doesn't).