The commander's tent required your corruption point to be 10 or higher to be able to unlock the special scene after sneak in his tent 3 times.
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The unmarked key isn't used for anything... yet. Future versions!
As for scenes that need high corruption to unlock, the mercenary commander's one is the only one. The blacksmith "suiting up" scene has a variation if you've got more corruption, however! If you've already got 10 points it'll be viewable in the gallery.