Ja.
I The Two Towers, Book 3 Chaper 11 (The Palantir), reser en Nazgul till Isengard strax efter att Pippin ser Palantir ut:
'Nazgul!' he cried. 'The messenger of Mordor. The storm is coming. The Nazgul have crossed the River! Ride, ride! Wait not for the dawn! Let not the swift wait for the slow! Ride!'
Senare i samma kapitel bekräftar Gandalf syftet med denna budbärare:
A messenger has been sent to find out what he is doing. And after what has happened tonight another will come, I think, and swiftly. So Saruman will come to the last pinch of the vice that he has put his hand in. He has no captive to send. He has no Stone to see with, and cannot answer the summons. Sauron will only believe that he is withholding the captive and refusing to use the Stone. It will not help Saruman to tell the truth to the messenger. For Isengard may be ruined, yet he is still safe in Orthanc.
Han spekulerar också lite på annan information som Nazgul kan lära sig:
It may be that the counsels of the Enemy will be confused, or hindered by his wrath with Saruman. It may be that he will learn that I was there and stood upon the stairs of Orthanc – with hobbits at my tail. Or that an heir of Elendil lives and stood beside me.
Så Sauron visste säkert att Isengard hade förstörts någon gång under eller senast strax efter Gandalfs och Pippins tur till Minas Tirith, och kanske har fått mer information.