It is safe to say if you play live with ANY pre-recordings (a single track to multiple tracks), therefore you are playing with Backing tracks. Now, obviously, the more tracks you use, the more unrealistic it is visually, but the closer to the real thing you sound (especially if performing cover tunes). This also includes using Arranger Keyboards (with styles) or Workstations with midi files/audio tracks etc.

So the question becomes, at what level is it considered 'cheating' for those who do not consider it 'professional' to use backing tracks? After 2 tracks? 3 tracks?

We can agree that someone manually playing left-hand bass and right-hand organ, while playing along to a DRUM TRACK ONLY, is putting in more 'work' than someone playing with multiple tracks/styles/Midifiles ... etc... but they are 'cheating' just as someone using Midifiles or karaoke. There is no real level where you can draw a line between these 2 examples. It's like asking when is conception - day 1, day 4 or day 7 ...etc.

Just my thoughts...