Like some of y'all said, The Storyteller was used soley for marketing. The reason why they used her along with Terra Cruentas is this:
The Storyteller, whose name is finally revealed in 2006, did have a presence in 2005. She might not have been in person as much as Terra Cruentas, but she was there. She was on billboards, commercials, the website, shoping displays, apparel, ect. The reason why Universal used her, along with Terra is basically due to Howl-O-Scream. Howl-O-Scream has been known to have icons that appeal to the GP, not neccisarly the fans. The icons for Howl-O-Screams tend to be "sexy". Sylvie, The Raven Twins, and House of Vayne, they sure all seem a bit sexy and scandalous. Even the evil DJ and the cell phone victim, while not "sexy", can relate to the GP with clubs with DJs, music, cell phone, and texting. So Universal decided to create a character along with Terra. Universal didn't want to follow in Busch's footsteps by making "sexy" icons. They wanted their event to look terrifying, edgy, and not for the faint of heart. So they created "The Storyteller". Since Universal must have felt that Terra was too "sexy", they decided not to advertise her, and stick to their path of being edgy and terrifying with The Storyteller.
*All of what I have said, basically came straight from my UTH tour guide. I asked if the theory of The Storyteller being used for marketing was due to Terra's costume not being ready in time for the commerical film was true. He said nope, and told me all of what you see above. In fact I'm second guessing his theory, due to the icon of 2005 being an evil jack-in-the-box in a child's bedroom. Evil jack-in-the-box... sexy? Unless it looked like Harley-Quinn or Chance, I think this theory is MythBusted. Also, Sylvie, House of Vayne, and the Raven twins were used way after 2005.
The Storyteller.... perhaps the most questioned creation by A&D.