Looks like NLog MIDI Synth is coming soon from these tweets:
NLog MIDI Synth”: Polyphony, velocity, pitch bend, mod wheel, sustain pedal & assignable MIDI controller to synth params. In AppStore soon!
Historic moment: The first synth app making your IOS device a real synth playable with MIDI hardware: “NLog MIDI Synth” submitted to Apple.
Another app with Line6 MIDI Mobilizer capability. Excellent news!