Shakuni was no devotee of Krishna. A true devotee of Krishna would never harbour so much hatred in their heart to the extent he has his sister's children all murdered in the battlefield.
Shakuni was an evil man who destroyed the Kuru Vansh. There was no favouritism towards the Pandavs. He was evil! End of!
The story of Shakuni being a Krishna devotee are stories which people make up as the years go on (like stories of Draupadi loving Karna).
I bet the CVs will make this story up in the end.