Det finns inga konkreta bevis för att de inte kunde
Ring-wraiths var män, vars död hade förebyggts av Saurons dominans. Den största av Ring-wraiths, Witch-King, var en kung av män och stor makt. Han var emellertid inte av folket av Elros av Númenor. Trots det var hans makt fortfarande mycket större än den unga Hobbits, Pippins, och bara från hans användning av stenen är det troligt att de skulle ha kunnat använda den men inte haft stor framgång med det. Det är också osannolikt, eftersom deras testamente dominerades helt av Sauron, skulle han ge dem chansen att använda den, eftersom han såg sig som en större kandidat för den.
Det var numenoreerna som hade blivit begåvade palantíri av älvorna av välsignade rike som hade besökt Númenor. De som lyckades mest använda stenarna var de som var "legitima användare", som var "Elendils arvingar" eller de som "ärvda myndigheter":
In the case of Denethor, the Steward was strengthened, even against Sauron himself, by the fact that the Stones were far more amenable to legitimate users: most of all to true ‘Heirs of Elendil’ (as Aragorn), but also to one with inherited authority (as Denethor), as compared to Saruman, or Sauron.
Unfinished Tales - Part Four, Chapter III: The Palantíri
Denethor kunde avskräcka Saurons dominans på grund av hans släkt, liksom hans stora viljestyrke och mental styrka, till skillnad från Saruman som snabbt föll i bedrägeri:
Saruman fell under the domination of Sauron and desired his victory, or no longer opposed it. Denethor remained steadfast in his rejection of Sauron, but was made to believe that his victory was inevitable, and so fell into despair. The reasons for this difference were no doubt that in the first place Denethor was a man of great strength of will, and maintained the integrity of his personality until the final blow of the (apparently) mortal wound of his only surviving son... And in the second place the Anor-stone was his by right, and nothing but expediency was against his use of it in his grave anxieties.
ibid.
Man kan dock riskera kontakt med en starkare makt rent av sin viljestyrka, som Denethor hade gjort, även om hans släkt skulle säkert ha spelat in i det här.
He must have guessed that the Ithil-stone was in evil hands, and risked contact with it, trusting his strength. His trust was not entirely unjustified.
ibid.
Det verkar därför troligt att även om Ring-wraiths sannolikt kan använda stenen, skulle de ha haft sin tanke och bedrägeri sedd av antingen Denethor eller Aragorn, eftersom de var rättmätiga användare av stenarna och skulle ha större makt till höger.
Slutligen, ett stort utdrag om vem som "rättvist" kan använda stenarna, den ständiga insisteringen på att dessa bara är de personer som "rättvist / lagligt" kan använda det föreslår att andra kan använda dem, men de som beviljades det genom rätt var mer framgångsrik.
These Stones were an inalienable gift to Elendil and his heirs, to whom alone they belonged by right; but this does not mean that they could only be used rightfully by one of these ‘heirs’. They could be used lawfully by anyone authorized by either the ‘heir of Anárion’ or the ‘heir of Isildur’, that is, a lawful King of Gondor or Arnor. Actually they must normally have been used by such deputies. Each Stone had its own warden, one of whose duties was to ‘survey the Stone’ at regular intervals, or when commanded, or in times of need. Other persons also were appointed to visit the Stones, and ministers of the Crown concerned with ‘intelligence’ made regular and special inspections of them, reporting the information so gained to the King and Council, or to the King privately, as the matter demanded. In Gondor latterly, as the office of Steward rose in importance and became hereditary, providing as it were a permanent ‘under-study’ to the King, and an immediate viceroy at need, the command and use of the Stones seems mainly to have been in the hands of the Stewards, and the traditions concerning their nature and use to have been guarded and transmitted in their House. Since the Stewardship had become hereditary from 1998 onwards, 15 so the authority “or again to depute the use, of the Stones, was lawfully transmitted in their line, and belonged therefore fully to Denethor.
ibid, note #16