I can possibly see Denney, but I doubt it. I think Ritzmann is gone, as his prior UDFA status and knee injury are too much to overcome. But if he DOES make it, it's because he's better than Denney.
As for Greer, I also doubt he goes, especially since I see the Bills keeping 5 CB's. And while he's light, he's the fastest Bill and that's worth something, at least in terms of development.