Not sure about tomatoes but half of Europe's strawberries are grown this way in poly tunnels - in planter troughs where the plant hangs out the bottom and the water goes in the top. They do grow towards light but the weight of the plant means they hang down. The do it because it saves space in the tunnels (you can grow a double or triple crop if you suspend some of the plants) and they're easy to harvest because the ripest juciest fruits hang down.