I meant the Hardened Veteran of Midway, sorry. The cheat will prevent you from getting the achievement on just beating one level for the "Hardened". In other words, you can use the cheat on normal and get Veteran of Midway "like you did." However, you need to beat every level on veteran for the Hardened Veteran of Midway to unlock. If you check in the thread you posted and check their gamercards, you will notice that most of them are missing the Hardened Veteran of Midway.
Honestly, I thought that it was hard as crap, but I eventually did finish it on veteran. Just check out the guides here and via googling for the best strategies. Youtube helped me out a lot as well.