The new music video made me think she might be pretty limited, but here is a cut from a The World God Only Knows character song album that shows Ao-chan actually can sing, at least better than many seiyuus:
The many, many scrolling comments are almost all quite enthusiastic, ranging from "cute" to "unexpectedly skillful." The lyrics are in Japanese at the bottom of the image. To turn off comments, click the balloon with three dots at the bottom right of the window. As usual with NicoNico embedded videos, it takes a while for the video to start after you click "play."
This song is called "Platinum," and is sung by Ao-chan as her character in the anime, Aoyama Mio. The album came out in December and can be purchased from CDJapan, among other places.
I can't say how much technical wizardry was required to keep her voice so close to being in tune.