Feeding your dog chicken and rice is perfectly fine and can help the dogs digestive system.
But you should also feed the dog some regular dog food along with the chicken and rice or alternate between regular dog food and chicken and rice.
So you can feed the dog chicken and rice everyday but every other day you should feed the dog some dog food but the chicken and rice diet is healthy for a dog.
Some vets will put dogs on a chicken and rice diet for some health problems so it's safe for dogs to eat chicken and rice and some dog food contains chicken and even rice.