Dog's do actually need some salt intake per day, but it's a very small amount.
Here is an article about Sodium & Chloride requirements for Dogs:
http://www.peteducation.com/article.cfm?articleid=686
Adult dog foods should contain at least 0.06% sodium and 0.09% chloride (on a dry matter basis). Puppy foods should contain 5 times that much. Kitten and cat foods should contain at least 0.2% sodium and 0.3% chloride (on a dry matter basis). Most pet foods contain levels much higher than these minimum daily requirements.
Deficiency:
A dietary deficiency of sodium and chloride would be extremely rare because most pets today are fed commercial pet foods. A sodium or chloride deficiency is more likely to occur because of an excess loss of these two minerals from the body. This can result from prolonged (or chronic) severe diarrhea and/or vomiting.
Toxicity: Sodium and chloride toxicity generally does not occur in normal animals with access to good quality drinking water. Any excess intake of sodium or chloride is filtered through the kidneys and excreted into the urine. If good drinking water is not provided, however, the concentrations of sodium and chloride can become too high. Signs of sodium chloride toxicity include seizures, blindness, dehydration, loss of appetite, and death within 24 hours.