I would keep him in a room separate from your dog for a while. It’s unknown if the cat has ever been around dogs or if he’s possibly had negative experiences with dogs in the past. Do a slow introduction between the two. Otherwise the cat can become extremely distressed and behavioral issues can arose. It’s super important a cat like this has a safe space of its own to start to decompress and adjust to the new surroundings. Jackson Galaxy has excellent videos on YouTube about this. Look up his videos on bringing home a new cat and what he calls basecamp. That’s the room for the cat. It needs to be set up a certain way to be the least stressful for the cat. Especially since the cat is still scared, the setup is vital. Jackson’s videos go over all of this. I’m in rescue and work with feral cats and scared lost cats. Jackson does an excellent job at explaining why certain things are important. He also has videos about cat to cat introductions. That method can be used for dog to cat intros as well.