Currently, it’s just me, and I would potentially be assisting with narrative and area design, as well as conversation editor suggestions and structure. Ultimately, we won't know the final logistics for a short while longer, but we'll keep folks updated - right now, it's solely design content work, which is one of Obsidian's strengths.
Beyond that it looks like they will be sharing the tools and development experience they have from years of working on complex RPGs (something inXile really hasn't done before). And he emphasizes that is still very much Brian Fargo's and inXile's game, they're still fully in charge, and Avellone and Obsidian will just be assisting them as requested.
Edit: Oh, and while it looks likely the Wasteland 2 Kickstarter will reach the $2.1 million goal for Obsidian's involvement, there still is a way to go, so please consider pledging if you're interested in the game or want to support Obsidian. The more money they get up front, the bigger the game will be when it comes out.