Salt in high amounts can cause kidney problems. Also dogs that eat salty food may then drink too much water and develop bloat which is fatal unless emergency treatment is given very quickly.
Salt used in pet food is used to cover up rancid meat and fat, and can cause kidney and heart disease, hypertension. It is used in cat food to encourage cats to drink water (another problem of dry food for cats).
Dogs that swim in the ocean can become very sick or can cause death, when drinking salt water. Homemade playdough that is high in salt can also be toxic.
It would be best to feed a pet food that is free of salt and don't give salty foods to your pets.