Nashville style would mean more country and western style of music. There is more 'twang' in the notes and there are some chord progressions which turn up more in country and western than other music. However, you don't hear ukelele played much in Nashville - though I'm sure somebody has done it.

Nashville is also a brand of ukulele. I would call the "style" bluegrass but here is a like to a Nashville ukulele. http://www.youtube.com/watch?v=jBkbZxHmn88