Dogs might be in the game as they at least do good here. Like the police etc, they make the dogs attack you, a cat for example, they can't do that. Imagine the police releasing a bunch of fierce cats rushing at you!
Me, I don't think we'll be seeing many more animals than fish, birds and dogs in the game. We're here to kill the people, aren't we?
I must say I don't like the cruelty against animals but hey, it's a game, and as long the animal do have a good role in the game(like a police dog) it's fine to me. :p