I don't know a lot about this, but I believe I have read many places that brine shrimp have no food value. I think people soak them in some vitamins before using them as food. I think some baby fish need the baby brine shrimp as a food source - I'm not sure why, if they have no food value.
They're safe just not real nutritious. Newly hatched baby brine is more nutritious cause they still have their yolk sack attached. Brine can make a great food for hard to get feeding fish until they learn to eat frozen. Soaking is vitamins is common, just to add a little nutritional value.