AniDB only shows Jun Maeda and Ga-Na (character design) as being staff members of Key. The two of them appear to be working on this as a side project. They show only Aniplex and P.A. Works for animation and main production. I would hesitate to say that the involvement of two people infers all of Key as it does for AIR, Clannad and Kanon.
Visual Arts, however, is on for production, and they are the parent company of Key. Key also has Angel Beats listed prominently on their website.
Still...they've made an awful lot of effort to separate out Maeda and Ga-Na during the promotion of this. It is more like how they separated Hisaya Naoki for the creation of sola.