Yes, the iOS version of Notion will allow you to connect a MIDI device to your iOS device and use it for real time MIDI entry. When you tap the record button, there is a metronome that plays the tempo of the song that you are composing for. When you play along with the metronome, your notation will be entered into the score. You will want to contact the manufacturer of your MIDI device for information on connecting it to the iOS device that you are using.