iOS connectivity with an Apple Lightning to USB Camera Adaptor (LUCA) is only possible with the second generation MX.

Blake is correct about the 1st version of the MX not being fully USB compliant, that is you can't send and receive audio on a USB cable, but the original MX can send midi data both ways to an iPad with a USB camera adapter. You can send midi to Yamaha's FM Essential app, Moog's Model D emulation app, or the Nanologue app on the IPad and it will play but only through the iPad speakers or headphone out: sound will not travel back to the MX audio outputs via USB. And sound from the MX will not travel to the iPad via the USB cable. The second version of the MX corrects that problem. With the right cable or adapters you could take the headphone output into an amplifier or a mixer for live performances. You can also use the USB Camera adapter to send midi data from the iPad to the MX. I've tried that with the MidiOnStage app. GarageBand seems to be looking for a Bluetooth midi device rather than one connected to the Camera Adapter so it probably won't work. Hope this helps you.

Added: I just tried the MX through the USB Camera adapter and it does pass midi info to GarageBand on the iPad so that works as well.