Arad's decision wasn't a simple one.
Deciding that their luck would run out meant that he wouldn't scare the monsters away. He would doom them to facing what would've happened if he had refused to come along.
Would he let some of them die? Would he protect them? Or would he pretend to fight and only help when needed?
Arad asked the old man for his opinion, and Zeus said to let them face reality. Scouts live and die in the mountains; their job is one of the hardest jobs a Storm Titan can do.
All of those scouts are hardened warriors who braved the deadly mountains tens, if not hundreds, of times. None of them is a weakling, and so they should all survive, if they are worth their salt.
One of the scout's main skills is detecting monsters before they can approach them and escape or prepare for a fight.
Arad was scaring the monsters from literally kilometers away so the scouts never had a chance to sense them, but they should be able to when the monsters get close enough.
