It is ok to use those dessicant packets, but I don't know if it is feasible seeing as that is such a small amount of dessicant! Those are just designed to keep the moisture out of the air in the box for whatever product, but for drying mushrooms there is a lot of water in the mushroom to be absorbed, so you are probably better off just buying some Damp-Rid, it is easy to get and cheap!

Yes they can be eaten at any stage of drying (water does not have an effect except to induce rotting if fresh shrooms are harvested and left to sit out).