It depends on what form of adamantium.
Adamantium typically, is almost impossible to destroy or fracture. From Marvel's background information on Adamantium:
Although True Adamantium was thought to be indestructible, there are
at least two known examples of the alloy within the Earth-616 reality
sustaining damage without molecular manipulation. The first involved
Thor focusing all of his strength into striking a small cylinder of
adamantium with Mjolnir, which only slightly dented. The second
incident involved a battle between Ultron and the Hulk. During the
fight, the Hulk punched the robot with enough force to slightly dent
it. (Both instances were later revealed to have been only Secondary
Here is an example of Hulk manipulating the shape of adamantium by squeezing it:
Hulk has fought Wolverine on many occasions. In World War Hulk, which may be when Hulk is the maddest I've read, they square off a bit, and Hulk understands that he cannot kill Wolverine. So he shakes him causing a lot of trauma to the brain, to basically knock him out.
This does have a lot to do with Wolverine's healing factor, but in the very same battle, he fights Colossus in steel form. With much ease, Hulk defeats him by bending his steel arms backwards, essentially breaking them, and removing Colossus from the fight. In no way does he attempt to do this to Wolverine's adamantium skeleton. Time is of concern to Hulk, and maybe that's why he didn't attempt to manipulate adamantium as such.
In Ultimate Wolverine vs Hulk, Hulk rips Wolverine in half. I'm sure there are other stories where Hulk has ripped a body part off Wolverine, but the weakness is not in the Adamantium, but rather the ligaments.
In regards to Hulk lifting Mjolnir in the Ultimate Avengers movie, which I asked, there is a great answer to that. In short, in the Ultimate version of Mjolnir can be lifted by anyone of sufficient strength, and has nothing to do with worthiness.
Yes, depending on what type of adamantium. Has it happened to Wolverine's adamantium? As far as I know, no it hasn't. Theoretically, I suppose it's possible as Hulk has access to unlimited energy the angrier he gets, but I don't think Marvel would ever completely settle it in-universe.