[White Council] When the White Council attacked Dol Guldur...

[lathspell]

I'm rather sure that Radagast was a member of the White Council in the beginning and stayed in it until the end. Yes, he became (or maybe he always was) enamoured of beasts and birds, but there are many ways to fight against Sauron. I think that most of the information about Dol Guldur and the ways of Sauron's servants came from Radagast and his animal-friends.

I believe Sauron send back some of his Nazgul to keep charge over the forced he left there. To leave Dol Guldur is one thing, he couldn't take the risk of being overrun by the White Council. To leave it behind uncontrolled and therefore in chaos is quiet another, so I think he send back Nazgul to order the troops there.

Oh, and I certainly don't think Legolas was at the challenge of Dol Guldur, or something would have been said about in LotR. I don't think Tolkien would leave out such an important thing.

greetings,
lathspell