AFAIK, that Adobe blog is the correct and latest information with regards to iOS and assets with code in them.
So the only SWFs which you can load at runtime are those which you've packaged with ADT during packaging time. This is because their ABC are compiled for iOS at that time, and their code is stored in the IPA.
So you'd load those SWFs with an app-local URL, like app://assets/level1.swf
You could load their bytes with the File class (./assets/level1.swf), and then I assume loadBytes would work.
It seems I've read that you can unzip the IPA and store those SWFs on a remote server, then load them at runtime and it works. But the key is that you have to load the SWFs which were packaged with the app, as they've been cross-compiled for iOS and had their ABC stripped out and linked into your app.
All this is to be compliant with Apple -- all code must have been linked at packaging time.