Sasuke's comment during his battle with Itachi regarding the possibility of Madara being alive. I am sure he used something on that kind of time scale, but alas, I could be wrong. Not to mention Madara didn't die when he was supposed to die, so I would put that as a maybe.
Tsunade, according to the wiki, is currently between 54-55 years old; the Third Hokage was between 68-69 at the time of his death. If we factor in that the 2nd passed on the position of Hokage after the passing of the 1st (ironically enough, the series makes it seems like Tobirama outlived Hashirama) then that battle had to have at least been 70-ish years ago.
That's still a long time in the open elements of the Valley of the End. The earliest Orochimaru could have gotten the DNA would have been maybe 40 or so odd years ago. The bloodstains from armor would have sufficed for Hashi and Tobi, which apparently the village kept if I recall correctly.
All in all, I think there would have been too much time passing for the DNA to have remained in a state that could actually be found and used for Edo Tensei canon-wise.