Yes:

http://techland.time.com/2010/12/27/gorillaz-reveal-what-app...

https://news.djcity.com/dstrukt-performs-i-heart-kanye-routi...

iPads are really compelling as an audio controller, particularly with great multitouch support.

Yes. AudioBus is a major iOS music platform.

Check out the list of compatible apps on their website, companies like Ableton, Korg, Yamaha, and countless indie devs take this seriously, and really, we all should.

https://audiob.us/apps/

ipads are used pretty commonly in it.