You cannot blame a cat wandering around and expect the animal to know (this is Mr. Badass' house with his big mean dogs, DO NOT ENTER) that's not how it works.
I wouldn't. I'd blame the owner for letting the cat wander around outside. My Dobe hated cats. If one got into our backyard while he was back there and got caught, I'd feel bad for the cat, but wouldn't blame my dog.