All Virtual MIDI capable apps can be controlled and recorded in Cubasis.
Have a lookie here:
http://www.iosmusician.com/2011/09/list-of-ios-apps-with-virtual-midi.html
Some of my favourites that I use are: Addictive Synth, Sunrizer, NLog Pro, Magelian, Wavegenerator, Arctic Keys, CrystalSynth XT, Korg iMS-20 and iPlolysix, Animoog and Casini to name the few.