That's certainly some wild speculation without any proof =)

Kelvin's story about going to save the world for DHARMA does seem to fit as he was expelled from the army he probably thought it'd be the best thing to do with his life. He at least once talked to Desmond about the Hostiles. We know the Hostiles don't seem to care that much about the button and the hatch (Ben called it "nothing") so I doubt if Kelvin was one he would've stayed in there all that time pressing the button.

Most likely explanation, Kelvin was a real DHARMA employee who was transported to the island to work in the hatch with Radsinski.