It doesn't matter at all whether someone is playing over a MIDI file backing track or over auto accompaniment provided by styles. If they can perform that is all that matters. And if it makes for great entertainment then they are definately a talented entertainer.

You just gotta do whatever is needed as a vehicle for a great performance and people shouldn't get hung up on what that vehicle is. If you can do it just using styles then go ahead but if you feel that a MIDI backing track would provide a better bed to play over then do that instead. Creating a high quality MIDI file backing also requires a special talent and performance ability and should never be criticized.