Nate,
If the trail official is properly "trailing" the play, they can ref "one play ahead" which means that you aren't focusing on the dribbler. You can still see the dribbler out of the corner of your eye and you would still notice if they palmed the ball real bad. But why would you be focusing solely on the dribbler (especially in 2-person) when they are 9 other players that need eyes on them?
Whether or not you wish to call that unguarded palming violation is up to you. Officials at higher levels often don't call a player for a palm or travel in the B/C when they aren't guarded. They aren't "wrong" for not calling it - that it is what they have been told to do by their supervisors. It might be a more appropriate call at the high school level.... maybe, maybe not.
Even at the HS level, I'm not calling an unguarded carry unless it's so bad that it sends shivers down my spine.
Z