That'd make their problem with having the dogs on set even worse. That technique relies on exact angles and actors performing in exact positions. Move an inch too far and the illusion is spoiled. That's asking a lot of doggies...

With motion capture, it's become a lot easier and much cheaper to create realistic animals than even a few years ago. They also have the option of shooting the dogs on green screen and composite them on the plates from filming (which makes it really easy to oversize them), using the 3D full CG dogs only for the larger or more complex action shots. I didn't pay attention to that, but I would not be surprised the attacking dog in ep. 2 was a VFX. All of this is costly, but so is filming with animals.