Depends on their Lead. Some are called in privately and commended... some leads will commend while at their team meetings in front of everyone I have gone to City Hall once and filled out the card. Hopefully he was called out and everyone heard how he made my son's day!
I don't know if it's the same in the parks as it is on Disney Cruise Line, but our waiters told us that the compliments and high ratings are directly tied to their promotions and raises.
We stop by City Hall at least once during the day and have the host there fill out a compliment form for us about CMs that have been above and beyond. It goes in their folder and is a factor in promotions, switching from Temp to Perm, raises, etc.