Council of Elrond

9) The Stones of Feanor:
DR: No hobbits may be played as characters.
WR: 4 different Palantiri have been tapped to use their specific ability.

A Palantir has been tapped to use its specific ability. But it is later discarded, due to a corruption test.
But, I think that it is still good for the scenario requirement ?

Yes, you are right. What happens to a Palantir after it has been used is not relevant for the scenario.