And yes, as far as I can tell it is possible to do this, despite one being a Vile Feat and the other bieng a Exalted Feat. Since they both have the same requirements stat-wise, a character only has to worry about the Vile/Exalted restrictions. As far as I can tell, a villain with the Dark Speech feat who turns to good -or at least neutral- could theoretically learn the Words of Creation. Th stipulations of Vile Feats is that only Evil can learn them, and the stipulation for an exalted feat is that you cannot perform an evil act while posessing one. So long as the reformed villain does not use any of the evil aspects of Dak Speech, he should theoretically be able to have both feats.
And why would you want both feats? Mainly for the resistance to Dark Seech, but I've been considering homebrewing a feat that has both as its prerequisits. Anyone have any advice on what it should bestow?
Also, when one person uses any Dark Seech effect, could another person theroetically cancel it out using Words of Creation, since the two are polar opposites?