:::::::To clarify, a digital copy of the Rachel Maddow Show is a credible source to report something said on the Rachel Maddow Show. But you're dead-on correct in what I think you mean, which is that it's not appropriate to support reporting the use of "teabagger" as an endonym throughout the article.  
 :::::::To me this isn't any different than the reasoning by which we don't report "some niggers", or "many niggers in the movement" to refer to people in the prose of the Civil Rights Movement article, even though many credible sources support Bull Connor (who is notable) referring to them that way. Like "nigger" for that article, the term is used pejoratively and obviously isn't worth reporting in the article, even though some Black people have at some time addressed each other that way. The same is true of possible documentation of some TPM people saying it.  

 :::::::Furthermore we wouldn't write "some political pundits have called the protesters "niggers,"" or "some in the movement have reportedly used the term to address each other." And likewise we wouldn't create a section "Use of the Term "Nigger"". Like "nigger" for the CRM article, "teabagger" is inappropriate for this article. It's pejorative and absurd that it be addressed. The measure of a good article is what's relevant. -