The Istari and Arnor's fall

[Inziladun]

Originally Posted by Aiwendil

It also occurs to me that they may not have wanted to reveal themselves too clearly to Sauron at this point, which is another reason their role in the war, if they had one, might have gone unnoticed.

I don't think Sauron was a consideration, due to the fact that they had no idea he had returned. As noted, they thought the power in Dol Guldur was one of the Nazgûl.