The spirit of the brother of Thor (the God Loki) was inhabiting the body of the Hulk in the shots from Hulk vs Thor movie. The might Mjolnir can only lifted by those entities that are deemed worthy....Loki is not worthy. In the shots posted below that from the first animated Avengers movie (that I also own) the Hulk was the Hulk and deemed worthy to lift Thor's hammer. Within the comic books both the green and red Hulk have lifted Thor's hammer (no homo).
Hulk's power is absolute. Loki didn't tap into it, into the anger. He couldn't. WHy would Hulk be deemed "worthy" to pick it up, when he meant to do Thor harm with it? Also, he was having a hard time picking it up. If one is deemed worthy, one doesn't have a hard time picking it up.