Right - Mew doesn't do anything to Tapu Koko, it puts a shield over the bench. Stealthy Hood puts a shield over the Pokémon it is attached to. So you'll just have two shields up and nothing getting through.
Now, if you have something that says 'This attack is not affected by any effects on your Opponents' Pokémon', then it would work (as it would ignore the Mew).