The Palantiri were created by the Elves in Valinor and given to the high race of Men.

The witch-king could in theory have used a Palantir, but there’s no suggestion he did.

The seven stars in Gondor’s crest are the Palantari, and in the War of the Ring, Aragon specifically requested they be added to his banner. They represent the highest level of the civilization of Men.