I once coached an XP (yes, that's eXtreme Programming) team through successful certification at CMM level 5. In many ways XP meets the values of CMM better than waterfalling does, and I've always found auditors understand that.

I've been very interested in CMMI and Agile for a while. There's a blog that I follow. He's done some interesting screencasts too. There's also several studies on marrying the practices together.

Ultimately, if you get the two of them working together properly then you can certainly use Agile to help achieve a CMMI certification.