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!