Nihilus is obviously a man,

 

How do you figure?

Really, in some instances, "man" is a generic term used to refer to a people or an entity. Like mankind human, "I saw a man. Nothing more." On the "Sixth Day," god created Man. I wish I could come up with more examples, but oh well. Using the term "man" is, sometimes a little more appropriate than using the term "that," "this," or "it."

Is anyone else tired of hearing about Darth Nihilus?

Pretty much, yes. I'm willing to wait for Kotor III and see what comes up, and if nothing else is said, then I'll use my imagination!