the vast majority of people on here report exactly the opposite...that they were NEVER able to substitute anything besides a piece of fruit (single piece, like a banana or the small prepackaged fruits like the kids' grapes or apple slices...but not the fancy fruit&yogurt or fruit medleys) OR a bottle of water. Most of the counter services are going to be pretty picky about not allowing other sides because the desserts are inexpensive pre-packaged items...usually less value than sides like salads or soup. Where were you at that allowed you to take a salad or soup for a dessert?
Now I have seen people allowed to get salad or a small cup of soup for a snack credit at resort counter service places...but the only salads allowed for a meal credit were the entree-type salads like the chicken Caesar salad