My dogs have eaten fresh tomatoes for 14 years! No problems ever. We grow them and thet love to go snatch them off the vine--lol. It just makes a mess with seeds down their fronts ( mostly my previous white chested shelties). I will give the Chi's little chunks to play with and eat...they love it--just not too much or you will get loose stools.
Rule of thumb on veggies...above ground growers loosen bowels, below ground growers firm bowels.
Mine love chewing a carrot stick, broccoli stem or the center vein you cut out of a collard green or piece of romaine! Yum...low calorie treat!