The first question is self-explanatory, and if the answer is yes, is Mountain Hammer and it's upgrades usable on such items without counting as sunder attempts? If not, can they be used instead of an attack in a sunder attampt?
[RPG] Is every attack against a weapon/shield a sunder attempt? (Also, Mountain Hammer relation to this)
Not every attack you make against a weapon/shield is a sunder attempt, for the same reason that not every attack you make after moving 10' or more in a straight line is a charge. A sunder attempt has a lot of rules (attack of opportunity, opposed rolls, etc) that a normal attack doesn't.
In fact, many attacks that don't pass AC are actually striking a shield/armor, and they won't have a chance to sunder them. It's an abstraction thing.
Now, the answer for "can I do a special attack as a sunder attempt" is more open to debate, and will almost always have to be at the DM's discretion.
As for Mountain Hammer in particular, it says "Target: One creature or unattended object", which would show that they specifically singled out "attended object" of the maneuver scope, so it seems RAI is "No, you cant", but again, DM's call.