I just ran "rum" 90 proof, 1 ounce through 3 independant nutritional databases. They all came back with ZERO carbs, zero protein and zero fat, and around 75 cals. I don't know where Atkins got their info from, but the source of the sugar used in fermentation is completley irrelevant.
I'm also not sure what BigAndy's teacher meant by "lowers ketone levels"? Perhaps you could clarify this in you next class? In non-diabetic males alcohol inhibits both gluconeogenesis and glucose uptake (the picture is slightly diff for women). If taken on an empty stomach with fasting glucose levels it will therefore hasten descent into ketosis for most people. More likely the alcohol causes a greater requirement for ketones as fuel so that something like a ketostix will show reduced ketone EXCRETION in the short term. Spirits are also strong diuretics which can also reduce the reading on a keto strip.