How to defrost frozen food in fridge
If this is all kept at refrigerator temperatures, then cooked, your health risk is extremely low.  However, there is a better method, which you suggest.  Place your seafood/shellfish in a colander or strainer. Place that over a container so that the melting liquid can drain off, and so that the product will not be sitting in the liquid.  The same set up can be used for fresh fish, and is common in seafood markets.  With non-frozen, the seafood can be packed with ice to keep it as cold as possible.  Again, with the set-up I describe, the melting ice will be captured below the product.