There's a Klezmer violinist called Itsak (or Itzack or Itsaak or something) Perlman who is trained as a classical comcert violinist. He's bloody good. I think, as has already been said, its about whether or not a musician has a 'feel' for the style in question, and that's down to how much they've listened and played, and maybe whether they have the humility to learn from the old codger down the road who's technique is lousy but who genuinely knows how to do folk. If they really appreciate the music and learn, then they'll probably be amazing-if not they'll sound like a classical musician failing to loosen up. (A la menuhin and grapelli recordings.) Unfortunately, to be a real virtuoso you might have to really concentrate on one type of music, so I'd say that really good classical musicians who cross over well are rare, but it's completely possible.

oh, and someone who fails to convey any emotion isn't a virtuoso however good his technique is.