There are a few (actually I should say were a few, as I haven't been there for a few years) that were hired off of resumes, but the vast majority are hired from personal recomendations. ADA is large enough that they normally just put the word out that they are in need of a couple of pilots and the present employees tell their friends and the slots are filled. Thats how I got my job there, and how I got 3 of my friends jobs there as well.
If your applying off of a blind ad, good luck but don't quit your day job!