Yeah, it felt like they were setting up Mickey as a member of Torchwood, but I guess Noel Clarke was committed to something else at the time they were filming "Children of Earth". Though, I don't think there's anything on the show that would contradict the notion that Mickey worked for Torchwood for a time. I mean, how else would he get to know Martha?

Wikis are my friend when I'm writing fic. It's always the case that someone has remembered the detail that I can't remember.