I think the inclusion of carnivorous animals would provide a dangerous thrill to hunting, because it creates the sense that you're being hunted yourself, by a creature that's just trying to do what you've been doing - survive. From a gameplay point of view, it'd mean you'd have to look out for more than zombies, especially in forests. I can imagine a scene like in I Am Legend, with Will Smith. You're zeroing in on a boar, then all of a sudden a group of wolves comes down on it. It'd give the environment a sense of livelieness, while providing a glimpse into what some animals are now forced to do.