Question about Hermit Crabs? Saltwater/freshwater?

No; for two reasons. One, you don't know if this salt contains the nutrients and salinity that the crabs need - Oceanic and Instant Ocean are two brands of aquarium grade marine salt that are acceptable to use for land hermit crabs (they are on the cheap side, and last quite a while). And two, depending on the salinity, you may be adding too much salt or too little salt - it's better to get the salt that is made to be used for marine life, so you know you are providing salt water with the correct amount of salt/nutrients.