In Federal Waterfowl regs "Sand and Shell Grit" is clearly stated to be legal to hunt over.
Salt is clearly stated to not be legal. If you buy Grit to put out and hunt over, look at the ingredients. It may have halite or Sodium Chloride aka Salt in it. If you use cheap Road Grit it is going to have some form of salt in the mix. Not all grit is "sand or shell grit" either.
Lets look at one storebought grit product.
http://www.morningbirdproducts.com/product_pigeongrit.html INGREDIENTS:
Limestone
Oyster Shell
Salt
Zinc Oxide
Iron Oxide
Monocalcium Phosphate
Dicalcium Phosphate
Calcium Carbonate
Sodium Chloride
Mineral Oil
Sodium Selenite
Zinc Oxide
Manganous Oxide
Ethylemerdiamine Dihygrodide
Ferrous Carbonate
Copper Oxide
Cobalt Carbonate
Calcium Periodate
ANALYSIS:
High in mineral content.
It does contain Salt, but also note the words "high in mineral content" Another commonly used name for grit is "mineral grit".
From TPWD Annual Public Hunting Lands definitions.
http://tpwd.texas.gov/huntwild/hunt/public/annual_public_hunting/need-to-know/#definitionsBaiting - The placement of minerals, vegetative materials, or other food substances used as an attractant for wildlife.
Though the wording was likely put in place related to Deer hunting, placement of minerals on APH public hunting lands is clearly stated to be Baiting on state APHP units. Most grit could be called a mineral or containing minerals.
So lets look now at the statewide migratory game bird regulations.
http://tpwd.texas.gov/regulations/outdoor-annual/hunting/migratory-game-bird-regulations/If you open the links for Definitions and Methods, TPWD migratory game bird regulations mirror Federal regulations therefore does not define grit as bait or hunting over grit as prohibited. So private land, you may or may not be able to use grit that is free of salt because you can't always use common sense with Hunting regulations.
I would suggest writing the appropriate authority for where and what you want to do regarding setting up a bird grit area and get it in writing or printable email first.