Personally I think some of the Weimaraners I've seen would qualify as blue (shading thither from a steel gray). And while it's hard to judge from online photos, I think a few of the deerhounds (especially Havoc and his sister Holly Golightly; scroll down about 2/3 of the way) on this page are bluer than any Ozark coon dog I've seen.

Some dogs are called "Blue", of course, for the sake of the rhyme scheme.

Liland