The early versions did contain meal. Here is a recipe for the one without meal: Athole Brose 2
Both Sir Walter Scott (1818) and Neil Gow (1840) spelled it Athole. This is followed in the OED.

Being American, I spell it whiskey, which also is the spelling used with the definition of athole brose in the Oxford English Dictionary.
The recipe is said to be very old (probably is) but there is no proof of the name "Athole brose" being applied before the 19th c. in writing.

The Stewarts of Athole descend from the natural sons of the Earl of Buchan, fourth son of Robert II of Scotland.
Also see Historic Earls and Earldoms of Scotland: Earldoms
The Athole Highlanders were the old 77th Highland Regiment of the late 18th century.

John Stewart was the first Earl of Athol (15th c.). I am not about to get into the problem of Athole vs. Athol (both ignorance and lack of interest on my part). Let the Scottish royalists fight over that. Whether any of these had anything to do with the Athole brose is unknown; the name may apply to the region near the Tay where the Atholes had lands.