Does yeast use the salt in the ferment?
Yeast does not eat or use salt.  Salt inhibits or retards the growth of yeast and too much salt can severely impact its ability to leaven or even kill it. ( all though modern commercial yeast is more resilient than naturally cultivated yeasts like in sourdough's ) 

Salt has an effect on gluten, it does not aid in gluten formation but it does ad strength to the gluten after it is developed thereby allow the dough to hold more of the carbon dioxide produced by the yeast. 

Yeast feeds on carbohydrates and sugars to produce carbon dioxide.

We use salt to enhance flavor. 

wikipedia page on yeast

king Arthur page on salt