In the Command and Conquer 3 PC demo, you can select Nod or Scrin in the skirmish faction menu while holding N or S respectively. But it looks to me like EA didn't think most players would notice this, so now we get playable Scrin, but no Scrin buildings or units in the demo's code. Therefore when you start a match as Scrin, you have nothing and you are declared defeated. (less info)