In my experience classically trained violinists play much louder than fiddler's - they deliberately use long bow strokes whereas a fiddler aims more for a rhythmic danceable sound which has more transients.

From this observation alone I would conclude that orchestral players should suffer more than fiddlers from violin related deafness. As I have never heard of such problems I think you can assume that you should be okay.

I've played fiddle on a regular basis for over 15 years now and my hearing still seems okay to me - mind you sometimes I don't hear my wife when she asks me to do some thing (especially when I'm humming a tune to myself - perhaps that's what you mean by deafness :) ).

Ian S