This cameo rumor comes from Floss Magazine's Twitter feed, but it has neither been confirmed or denied by Christopher Nolan's camp or anyone at Warner Bros.
Here is the news:
Surely some will welcome this idea if it is true, and others will balk as Adam West offered one of the campiest renditions of the Bruce Wayne character ever committed to film. There is no mention as to what character the actor will be playing. Anyone who has seen Baadasssss! knows that Adam West is capable of giving the weighted dramatic realism that Christopher Nolan demands in his Batman movies, so this might be fun.
The Dark Knight Rises was released July 20th, 2012 and stars Tom Hardy, Christian Bale, Anne Hathaway, Liam Neeson, Joseph Gordon-Levitt, Gary Oldman, Marion Cotillard, Morgan Freeman. The film is directed by Christopher Nolan.