Diablo – Do ruby-socketed helms work for Paragon experience

No, you do not have to use the weapon to get the kill.

The majority of the games characters do not directly use their weapons in their attacks. Most of them are just ways to bolster stats and give a baseline for damage. The monk, for instance, is a highly melee focused class, but does not use his weapons (unless they are fist weapons).

That bonus you see on the weapon is added to your cumulative bonus total.

It works exactly the same as a helm ruby. Both items increase the "Bonus Experience %" stat on the character sheet. Despite the somewhat confusing name, this is a % increase to the base experience gained for each kill.