Well seeing as I currently reside in vegas and have for a year now let me put all of your curiosities to rest,with a list of all the places in that game that are real.
1.Nellis air force base.
2.Lake Mead.
3.Boulder City.
4.Hoover Dam.(God I hope you knew this.)
5.McCarran International Airport.
I can't think of any more atm because my brain is shut off. :cryvaultboy:
Adding to that, the "Freeside" sign is actually the defaced sign for Freemont St. which does exist (it's where all the downtown casinos are)
The Silver Rush in freeside is probably the Golden Nugget, a casino located on Freemont St.
The Atomic Wrangler doesn't appear to match any casino directly. Binion's is across the street from Golden Nugget in real life.
And many of the casinos in The Strip are based on real ones or an amalgamation of real ones.
The spade-shaped sign for Gomorrah resembles that of the Sahara (now demolished) but the fire motif outside is reminiscent of the volcano in front of Mirage.
The Tops' might be based on Circus Circus with the front entrance the way it is and given its location on the strip (plus "big top" is slang for a circus tent) but given that it's home of the Rad Pack, it clearly draws inspiration from The Sands (also now demolished) as well.
Ultra-lux seems to copy the design of Bellagio (the giant curved building, fountain in front), though the fountain is drastically scaled down. The baths inside and the design of some of the interior area are references to Ceasar's Palace. Naturally calling anything in New Vegas "Ceasar's" anything would be very politically unpopular with the locals...
The Lucky 38 is the most obvious of the bunch, based clearly on the Stratosphere, a massive tower with a rotating restaurant up top (and amusemant rides now, you've never ridden a Scrambler ride until you've done it staring 300 feet down at a parking lot).
What amazes me is that they're actually roughly in the places they ought to be, from the airport south of the Strip to where Freemont St. is.
There's also a very subtle in-joke with the NCR monorail. A monorail line DOES traverse the strip, but it doesn't go to the airport in real life, and that's one of the main reasons it's hemorrhaging money despite being heavily funded by the strip casinos.