Yes, gerbils can eat salt but it is not necessarily healthy for them. Very little amount of salt may be beneficial to some extent however.
Gerbils love salty food like nuts, sunflower seeds and potato chips. They are high in fats but very low in calcium and other needed nutrients. Giving gerbils lot of these food can make them unhealthy and sick. They should only be given as treats once or twice a week. Salty nuts should be thoroughly washed before you give it to them. Healthy balanced diet of food pellets, fresh veggies and fruits should be provided every day.
Small salt sticks are sometimes good as it helps in the digestion of food. But if ingested too much, salt can be dangerous to gerbils. Eating salt or salty food increases the risks of gastric problems in Gerbils. Concentrations of the salt in gerbils alter the environment of the mucus glands in the stomach. This can sometimes lead to glandular stomach cancer.
Giving gerbils mineral or salt wheel is not a good idea. Bleached and glued together using chemicals, salt wheels are unhealthy for gerbils. Give them natural wood chews instead. Flavored ones can be bought at a local pet store. However a small salt lick and grass can be helpful as it helps them digest their food.
Salt or mineral blocks should only be given if for your gerbils are not eating the nutritious food you provide them. Some gerbils do not eat the nutritious food you provide them. Only then you may provide your pet gerbil with mineral or salt blocks.