I don't see how it adds anything meaningful to the game.
You're playing a soldier, shape-shifting into a dog feels out of place. I could see it possible as an AI unit that you purchase and it follows you around (until you enter a vehicle, then it goes away), but playable? Too many issues from aesthetics, to immersion, to gameplay. You'd need a whole new infantry controls and physics system to support it properly, such as support for forward-strafing movement animations.
Further more you'd be crossing into AR territory too much. Personal opinion: dogs are the least fun AR 'infantry' unit at the moment due to all the various issues that come from controlling them as well as their unit role simply not being very fun (especially not on the receiving end).
Lastly, another personal opinion; I know it is a game, but I never feel good about killing animals. I feel that games which do it go from "funny" to "couldn't they think of anything else?".