The short answer is yes, that Really is Emma Watson singing. The actress opened up about the "terrifying" experience during a print interview with Total Film. "I sing, so that's Really unexpected," she said. "I've never had to do that for a film role before, and I think people will be interested to see me do something very different like that . . . It gives me a different challenge, really." Disney corroborated the fact when it tweeted the aforementioned clip, a snippet from "Something There," saying explicitly that she's singing.
But wait, there's more! **t only is Watson using her voice for the movie, but her live vocals are used in several of the various numbers. In a separate interview with Collider, Luke Evans shared a fun tidbit about the musical process. "We pre-recorded every [song], but some of us sang live on set as well, during the takes," he revealed. "We were mic'd, and they recorded that, and I think afterwards, in sound, they'll be able to chose whether the live version is better than the pre-recorded version." So there you have it. In addition to all her other magical skills, Emma Watson sings. You can even hear her on the soundtrack!