It is allowed. DP uses this too but it only appears when you're not logged in just below the first post.
Yes Yes I am using it. But only the first ad spot gives most money. But what it does it grabs a good space and is totally viewable easily, so since its clearly viewed, i get clicks And this ad spots gives most CPM money
yeah its allowed and give you a good ctr, but this can abuse your site looking and disturb your traffic