Mike is the Brain-Damaged Victim of Foxy The Bite of '87 incident is a something referenced by Phone Guy where one of the animatronics bit the frontal lobe off a child. It's widely assumed this was Foxy, the disused, out of order robot of Pirate's Cove with the sharp teeth. Phone Guy is quote clear that the victim lived.
It's possible Mike is that child. One of the symptoms of severe frontal lobe damage are extreme risk-taking (This job for instance) and the rapid eye-movement seen in your compulsive checking of the cameras. There's also the fact that Mike is paid $4.00 an hour, clearly below minimum wage.
You know who can be paid below minimum wage? The disabled. It's a law designed to incentive employees to hire lower functioning adults to give them something productive to do. In fact, Goodwill was thrust into the national spotlight on the subject when it was revealed they were paying a blind employees $3.99 an hour.
Wouldn't severe brain damage count in this category? Perhaps Mike is the victim come home to face his attackers.
It's all confusing and strange, but utterly remarkable that such a simple game has left enough of a mystery around it to enable such speculation. Hopefully we'll find out more when the sequel comes out.