It is my understanding that chickens need good ventilation more than warmth. If this is a winter plan to keep the greenhouse warm I think the amount of ventilation you would need for the chickens would work against the warmth you need for you vegetables.
An alternative way to integrate chickens with greenhouses is to have them close together so that it is easy to transfer manure and
compost from chicken coop to greenhouse. As it breaks down it releases warmth and CO2 - both of which are great for plants.