Sauron possibly new that the Istari were Maiar, but he probably didn't know their true names, save, maybe, Saruman. Yes, they all had their different strengths. For Gandalf/Olorin it is Wisdom, for Radagast it is the creatures of the earth, etc.
Sauron used anyone who had a Palantir to his uses, there just happened to be one in Orthanc and Saruman used it, as there was one in the Tower of Ecthelion and Denethor used it. Sauron used both to control the actions of these two great beings. And, isn't it strange how, seemingly, the Maiar that were under Aule's rule fell to the dark side?
|