I'm looking at photos like this:
Slightly darker than typical skin tone, full lips. It's possible that no one who draws cartoons knows that black people have varying skin tones, but if they do, this could very well also be a black guy, certainly he didn't get these features from an European ancestry. The fact that Clancy Brown is pasty white and in no way olive skinned doesn't add any credence to this 'looks like clancy' theory. Now it is true that he got lighter by World's Finest and continued to lighten through JL and JLU, but even then, he's a shade darker than the other characters. But, I'd love to see/hear this discussion with Timm about his ethnicity.
What a curious example! Ving Rhames' Kojak was also based on Telly Salavas' Kojak, but true to the English language, 'based on' is not a synonym of 'same race of.'
If you've been over it a lot, it may be best to have that link to whatever Timm said around.