One of the main benefits of a tube fly is that it allows you to use a large fly but avoids the problem of leverage associated with a long rigid hook.
I'm not familiar with air brake line, so can't comment specifically on it. If it bends easily under an angled tension (imagine how the angle changes as a fish moves up and downstream of you during a fight), there isn't a leverage problem.
If, however, the tubing is quite stiff, you need to think further. If you can contrive that the hook pops out of the end of the tube using Dana's method, that should be fine. Otherwise, use the soft tubing suggested on the 'method to tie hooks behind tubes' thread (silicone rubber tube is widely available over here for this purpose). This guarantees an articulated fly, but still holds the hook in alignment.
In practice it probably won't make a difference for most of the fish you hook. Trouble is, it's the big ones that fight longest, and the long fights are where the effects of leverage may start to show...