If a druid at level 12 takes the form of a Gravesludge ooze would it get this benefit of its normal attack?
Swift Slam (Ex)
A gravesludge can attack twice with its slam attack as a standard action.
You only get the benefits listed in the spell. That does not include this "swift slam" attack, so no, you wouldn't get that.
Basically, all the wildshape and other polymorph effects act more like you in a monster suit, rather than you turning into a monster of that type.
Agreed; you'd still get to use two slams for your full-attack, but your standard attack would only be the one slam.