Salt is safe and often used as a thickener, but it can certainly be drying, depending on the specific formulation.
For my hair (which tends toward dryness), I have to be careful with salt, seawater and avoid all products with salt high up on the ingredients list.
(Examples of products that, unfortunately, really dried out my hair badly and caused massive tangles: Lush Big Shampoo (coarse sea salt as first ingredient) and John Frieda Luxurious Volume Touchably Full (sodium chloride as fifth ingredient).)
I think salt can be a good ingredient for providing relief for scalps that tend towards SD, fungal issues and excessive oiliness, it's mildly antimicrobial and antifungal.