Phil, one of the joys of harmonic progressions and variants of them is that you can, for example, actually play notes from one scale against a different scale and get an interesting and exciting sound - even to the extent of discord. It's all in the ear and taste of the musician.

If you listen to "Glen Kabul" by Old Blind Dogs, you'll hear a tune played in one scale set against chords from a different major scale - I forget which, to be precise, but I know that our band plays it in A major with, I think, a Gm set against it. Great stuff - and apologies to anyone if I have the exact keys/chords wrong!

Anyway, the point is that melodic notes don't necessarily have to mesh with the harmonies which underpin the tune. Tensions can be created and then resolved.