One of the most popular genres of music playing in casinos (and for a good reason!) is smooth jazz. The slow tempo is excellent for creating a calm and peaceful environment but varies from classical music; it is a little more upbeat without being too distracting.
Live music is happening around the clock in Las Vegas this is the Entertainment Capital of the World, after all! If you're looking for some quality live tunes in the destination, there are more than enough venues fitting that bill.