How do I connect my Alesis iO2 Interface with video camera Nikon D3200?
Im unfamiliar with the iO2, but it sounds as though you're basically wanting to use it as a preamp; you almost certainly can set up it so the inputs are mirrored back to the outputs so you can use it this way, but you will may  need some sort of audio application 'in the middle' to do so.  You'll also need need the computer running for it to work.

Thing is, though, this doesnt really sound like a particularly great way of going about recording your audio, and its certainly not advantageous to have to cart around, and hook up, a computer, just so you can basically misuse a USB soundcard as a preamp.  You'd be better off with a separate preamp.

Plus, if you were utterly determined to use the computer for some reason, you'd probably be better off using it to record your audio, rather than the camera; you'd be opting out on two extra stages of conversion between analog and digital for a start.
I think you're going about this the wrong way, though, and a separate battery-powered preamp would  be a simpler, easier approach.