The perimeter doesn't seem terribly secure, but there's a lot of warm bodies. His best bet for getting in is to stage a distraction of some sort, and slip past the green troops, which shouldn't be too terribly difficult (A Bluff or Sleight of Hand check, DC 14, ought to be enough to distract the guards on the outside long enough to slip in unseen; otherwise, you'll take a 5 point penalty to the DC 17 Stealth check to get past them.)