hey Lexicon,
Audiobus is simply an APP to transfer Audio. No MIDI data included. IOS itself has a MIDI transfer interface build in, called CoreAudio. So you can exchange Midi data in both directions. From Cubasis into an extern App as well as from the App into Cubasis. To record the created audio you certainly need Audiobus, which will add an audiotrack in Cubasis.
So all your usecases should be fulfilled.
kind regards
Ludwig