Decoy Drones have the description: "Tough, armored vessel with no significant guns. Attracts all fire from enemy ships to itself in place of ships within it's protection area.", but they have an armor of 0 and are ultra-light hulls, which doesn't match mesh up with the description of being tough and armored, but they do have 200k health which is probably fine for that statistic.
As a another possible issue, I just did an attack on an AI system with all 9 I could build via a Fabricator, and while my losses in the attack were small as it was, I lost none of these guys at all. I'll have to try them out more to see if it was just odd luck or if they are not working properly though.