Frankly, musicians use tones other than the diatonic tones in a key all the time. Half-step connections, flat and sharped 5ths 9ths and 11ths, not to mention juxtaposioning whole tone, diminished scales/chords, not to mention downright imposing other diatonic/other scales over "traditional" scores. Tell me those musicians are using a "one key" mentality and I submit you "don't get it". They may resolve these strokes of rebellion to satisfy the listeners desire for "relief", but then again, some musicians don't give a damn about it. However, how does one even begin to understand these relationships unless they "know thy fretboard".

To illustrate, show me a series of chromatic doublestops on two strings through ALL twelve frets, that is a round of 5ths, using ONLY b7ths and thirds.