I think is "no" and they don't add that place. Big Empty is just reference place by Dead Money and the location is next to Sierra Madre.
I dunno, I distinctly remember getting +1 to the challenge that says "learn about your future travels- all the way to the end of the road" when I talked to Elijah about the Big Empty.
Plus, he said the Big Empty had a lot of Advanced Pre War tech in it, including the foundations for the advanced stuff found in the Sierra Madre, like the Ghost People's Hazmat Suits, the Holorifle, the Holograms, and the Vending Machine.
He also implied that was only the tip of the iceberg, that there was a lot more great stuff there. So why not have a DLC located there? It would give us a chance to get more holorifles, maybe even other holo-weapons, a holographic companion perhaps, a cool STALKER style Hazmat suit, and much more hi-tech stuff.
The Big Empty could perhaps be the Fallout version of Area 51, I mean, it's in the middle of the desert in real life- that sounds like a "Big Empty" to me. Maybe most of it is preserved because the vast desert keeps most people away from it.
The Big Empty also sounds like it might be the Fallout version of Silicon Valley, what with hits high density of tech and research facilities. Of course, there's not as much silicon involved, considering that vacuum tubes are more prevalent than microchips, although I do believe that I read somewhere that the Fallout verse DID invent the microchip/semiconductors, just much later than we did IRL. You can also see what looks like wafer-thin computer components in the pile of "scrap electronics".
Either way, Area 51 or Silicon Valley, I wanna go there!
Plus, you might find evidence of whatever Elijah, Ulysses, and Christine were up to there before, which would be a nice tie in to Dead Money as well as further foreshadowing of the Divide DLC that we all know is coming.