It seems to me that if it worked with tomatoes it should work with zukes, squash, and peppers. Peppers vine less, but they can get very leggy.

I am planning to grow four pepper plants upside down after reading that they do just fine. But I decided not to go with squash after reading that it doesn't do well upside down, I think because of the weight of the fruit. Peppers are not individually so heavy in relationship to the plant.

But that's only what I read. Maybe someone who's tried it will give you a better answer to your question.