Guitar can cover all manners of guitar! You don't need to specify more than than that. Just like drums will cover a kit as well as bongos or whatever might be appropriate.

We definitely have the same thing in mind. Violin could potentially be used in rock, punk, electronica, or anything that might make sense. Yellowcard was one of my favourite bands growing up so I've certainly seen the charms of mixing classical in there. There is good potential for classical influences in a number of genres.