gman is not related with aperture. it doesn't seem like he's human, and given the lack of combine presence pre-cascade it doesn't make sense for aperture to be combine related.
perhaps portal is set during the early portal storms? damage caused to aperture facility, combined with possible...
so if a portal has been opened, presumably linking earth to the combine universe, what possible use would the knowledge of the combine world's location be to the resistance?
curious.