I never really read Dru that way. I suppose it's possible (it's been established that Slayers have some degree of seer-like abilities), but like others have said, I just always assumed that Dru was a natural seer. Interesting question though, I always kind of wondered what would happen if a Slayer became a vampire.
Why not ? in the first episode of buffy we can see that buffy makes stranges dreams....perhaps dru was promized to became a potential ! i think it's possible we won't never know it....