Stayed at Lower Forge 4-27-13
Sites 1, 2, and 3 are wide open group sites. Site 1 is closer to the latrine, 2 is right in the middle of the open area, and three is over closer to the water. No real trees at any of them to speak of. You might be able to scrape together enough trees to hang by yourself ... but I wouldn't even count on that.
Site 4 and 5 are the best options. Plenty of trees at each for multiple people. I don't know which I'd say was better of the two - but either one would be fine. And if you're going with a group of people, get them both if you can, and you'll have your pick of the best hanging Lower Forge has to offer.
Site 6 and 7 both have a few options. We stayed at site 7 and if the guys we met that were staying at 6 (who also coincidentally had a hammock) hadn't offered to let us set up a little bit into their site, we wouldn't have really had enough trees for the three of us. Site 6 has one good set of trees, site 7 has two decent sets of trees (though make sure you don't have really short whoopies) and there's a pair of trees that sort of span the two sites.
Sites 8 and 9 are again more open, and lacking in trees. You might be able to find somewhere to hang here - though you'd have to be edging into the woods a bit. Not really and pairs of trees of the right distance in the sites themselves.
So to sum up, sites 4-7 are hammock friendly. But aim for 4 and 5 if you can.