Given Shade's post (which was very good), I'd assume that these could trigger on glancing blows.
Another thing to note is that a Vertigo weapon won't be doing anything for you except when you are tripping, while a Weighted weapon will as there will be a % chance to stun stuff with all of your attacks. The trade-off, though, is that your DPS will be somewhat lower otherwise due to the poor stats for bludgeoning weapons.
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