Her voice actually sounds like Ashley's, although that may be in my imagination. I don't think her combat role is going to be anything like Ashley's, though, since she's supposed to be some uber-powerful biotic. My only beef is that I hope they're not so fixated on the tattoos-and-scars thing that they won't let you change her armor, because I'm going to be annoyed if she's running around in those straps for the entire game.
So the brief opening of that video shows 10 spots for party members. We have the three revealed already: Grunt, Thane, and now Subject Zero. We also know that both of the characters from the iPhone game, Jacob and Miranda, are in ME2 as party members. I've also seen that Bioware has more or less confirmed that Tali is going to be a party member, but it's not clear if she counts as one of those 10 because she's not a new character. Which means we have at least 4 and possibly as many as 7 (if Tali doesn't count as one of the 10 and the initial Bioware estimate of 13 party members was accurate) characters left to be revealed, including characters from the first game.