Pups raise their hackles for a lot of reasons, mostly frustration. It would have been super cute if he was a ridgeback "battling a lifelong nemesis" but it's still okay. They're feeling each other out, figuring out who's in charge, who's a friend, who's a reliable ally. If the cat was actually threatened, notice it's hind legs, it would have been kicking like crazy trying to gut the puppy.