Fruit salad with tomatoes
I have eaten a salad that included watermelon, tomatoes, feta and black olives. I thought it was... ok, not earth shattering. Also I made this Cherry/Tomato bite, which is in that genre, and certainly was interesting from a taste perspective. There are no rules, you can do whatever you like, you just have to determine if it will taste good. Personally I don't think I'd like tomatoes in a "standard" fruit salad.