If you are using live rock then the bacteria and other organisms in the live rock will seed the sand bed. I only recommend live sand when someone is starting a tank with all base rock, to start a bacteria line. Other than that I haven't seen any advantage to live sand for the cost.
That brings up another question from me...the "base rock" I have been looking at fuji live rock some of it does say "base" I took that as what should be on the bottom because it doesn't look as nice, is it that it doesn't have as much live stuff on it???