Obviously chickens will not eat tomato plant foliage as it is poisonous to warm blooded species, and chickens know what is edible what is not.
But they will scratch and dig up all the plants and ruin any vegetable garden quick.
Personally I found my chickens very beneficial for my citrus and peach trees.
I have about 10 citrus trees, 5 of them grow in the bounds of chicken run, 5 of them grow beyond chicken reach,
The ones "blessed" by chickens are greener and bear more fruit than the other ones although I fertilize and water all of them as needed.
I guess chickens destroy all grass and weeds competing with trees, also by scratching they instantly cultivate the root area and obviously the roots get constant supply of chicks poo fertilizer.
I also quit spraying my trees, since my chicks make sure there is no single bug on them like white flies, aphids or else.
Trees are happy and pay back giving chicks shade and quick hide from hawks.
Another word perfect symbiosis.
So forget about chickens in your garden, but move them to your orchard!