In the classical sense, “skeuomorphic” design is when an app’s UI looks like real-world devices. That’s what Logic Pro X is steeped in. Dials on amps in the application look like dials on amps do in the real world.
However, the term has been used to describe things like linen in iOS. With iOS 7 and OS X Mavericks, Apple has stripped most of that away. The changes the company in this regard are well-founded and welcome.
However, I don’t think that move means Apple had to follow the same path in Logic Pro X. In short, I think Apple views skeuomorphism as acceptable, as long as it’s functional. In Logic Pro X, it is. Switches, faders and knobs make sense in the world of professional audio, so Apple has switches, faders and knobs in its professional audio application.