Never thought of it as cheating, since it really is an old technique. The shredders simply brought it to a new unheard popularity of sorts. High gain Pickups and amps allowed for a lot of the sound.
Check out the guy in this amp demo. It starts kinda lame, but near the end, he has a great example of tapping to mimic a piano. Cool, not cheating, but not used everyday by 14 year olds in a pentatonic minor at GC
YouTube - Roland CUBE Street Battery Powered Stereo Amplifier
Oh, I bought the amp too, but still can't play like him................