It's true that there wasn't enough cha cha in the cha cha -- Amber & Derek dodged a bullet this week, probably because the show didn't want the judges to be sourpusses right out of the gate, with so many uplifting stories to hawk this season.
And I think the thing that gives Amber an edge isn't whether or not she's had dance lessons, but the mere fact that she's been drilled by choreographers fairly regularly over the last 4 years. The Glee cast has even gone on tour (and sung and danced live before thousands) in between seasons.
The steps she did on Glee may have been more movement than dance, but it's already in her head that she has to extend every limb, every finger, etc. Her ability to pick things up quickly-and-move-on is exactly the thing that every DWTS star needs to have, or develop quickly, in order to keep advancing. Derek remarked on this in that interview, and it makes sense that he's now going to throw the kitchen sink at her -- because she is already practiced in taking that kind of direction.
I just hope Derek doesn't treat every ballroom dance the way he approached the cha cha. And I'm speaking as one of his biggest fans.