if you are asking if Hotwire or Priceline only offer rental cars that are on site, the answer is no. As the PP stated, Hertz is a short shuttle ride away, but don't let that scare you, it is still a pretty quick process.
With Priceline you have no clue who you get until you have already paid. With Hotwire, you see the rental agency after clicking on the rate, but before booking. I personally have found better rates using the last minute deals at Alamo or National.