1. Combine juices and honey in a small saucepan. Scrape seeds from vanilla bean into saucepan; discard bean. Cook over medium-high heat 3 minutes, stirring until honey dissolves. Remove from heat; pour into a 1-cup glass measure. Place in freezer for 15 minutes to cool.
2. Place grapes in a large bowl. Add cooled syrup and mint to bowl; toss to coat.