Actually, Kevin the Shirt Murderer does lead some traditional English songs, although the odd verse or two from Quadrophenia slips in.

And Ruff -n- Reddy have been heard to sing different notes from each other, sometimes in the same scale.

I think you'll find Jumbo Gumbo feature walls of nasal corrupt French sung traditionally a fraction sharp - unless that's the exceptionally wide tuning on a cajun accordion confusing me (as Jon Loomes used to say "Give me an A. No, only one")