Oh definitely. We've "bumped into" princesses all over. We met Tiana in New Orleans Square. Snow White by her wishing well near the Castle. We met three princesses at Fantasy Faire. We met Jasmine and Aladdin at the back entrance to Tiki Room. Brave was big during our last trip so there was a meet and greet setup by It's a Small World to meet Merida. We LOVED the Rapunzel show at the Royal Theatre.
Honestly, some have specific meet and greets setup but we've ran into others without even trying. I love Disney magic
You'll often see other characters from Princess movies too. We ran into the Fairy Godmother more than once. The evil step mothers are a hoot (boy do they have the GLARE down good). Alice isn't an official princess but we've seen her and the Mad Hatter often too.