Here's the Heart sisters words at EW.com:
http://hollywoodinsider.ew.com/2008/...-responds.html
It's pretty clear that the sisters asked the RNC to knock it off, and more than once.
More than that, from the look of things, it appears that the only permission the RNC obtained was paying the ASCAP fees to play the song at the convention, but there's a pretty obvious difference between a license designed for restaurants playing music at as background, for example, and the producer of a nationally televised event selecting a song to be the leitmotif of a new star.
The RNC didn't obtain real permission so much as just get enough of a legal dodge set up to weasel out of any consequences for themselves.
And as the Wilson sisters pointed out, it was a pretty ironic choice of song anyway.