I was just wondering about this myself. Boxarox is a third level paladin, about to reach fourth. I am thinking about taking the oath of vengeance. Additional uses of smite evil does look better than channel energy. It seems reasonable that the allies' use of smite evil would last until the end of the day when the paladin gives them the ability. But this character is PFS, so we can't just house rule it.
I'm gonna hafta be careful. If somebody looks bad, but he really isn't bad, and I kill him, am I bad? I don't wanna do bad stuff. I wanna protect good people from bad people, and bad monsters, and bad things that aren't really dead.