I agree with Smokin that there are no health issues at all. The amount of salt used is not huge, the cure time is relatively short, and the product is thoroughly rinsed prior to cooking.
Coming up with percentages is essentially impossible. Percentages, or ratios, express the relationship between 2 or more items. With a wet brine it's the relationship between water and salt. In this case, I use a 5% ratio, e.g., 1 ounce of salt for every 20 ounces of water.
With a dry brine, you're dealing with only one item, salt, so no relationship as a percentage or ratio can be expressed. The term dry-brining may be technically incorrect. Pre-salting might be more appropriate.
The amount of salt called for depends on the weight and size of the item with time then factored in. Trial and error comes into play, as well as a lot of Googling.
For something such as a turkey, I use a ratio of 1 tablespoon of salt for every 5 pounds of bird. A 3 day cure seems to work best for birds in the 12-15 pound range.
On something such as a thick cut rib eye, I don't measure, but sprinkle on enough salt so that it's well coated, but not buried in salt. If I had to guess, I would say I apply around 3 teaspoons to each side of the steak. I then let it rest for 1 hour for each inch of thickness.