Django played a fretted instrument which enabled his intonation.
Louis sang with a scratchy voice that no one (myself Included) seemed to mind.

A lot has to do with personality, phrasing, note selection, rhythmic emphasis and cognizance of the style of music.

You could say that Tommy Jarrell was scratchy and intonation was dodgy but highly listenable if you are into Appalachian or Round Peak styles.

Since the tempered scale, playing out of tune has been modified but not solved.

Some ears can pick out tonal discrepancies even in pieces that are deemed to be in-tune.

Folk fiddling is a different set of criteria than classical violin.

Moral: Every style calls for different criteria in what considered good.