Hi Mahalo!

Sucralose is not a sugar alcohol. Those usually end in "ol" and include things like sorbitol and maltitol.
From what I can tell, the Atkins shakes don't have any hidden carbs in them; the calories from fat and protein pretty much add up to the total calories listed on the package, but if artificial sweeteners of any kind are a problem for you, you might want to avoid them or try a protein shake made with unsweetened whey powder.
For more information on artificial sweeteners and sugar alcohols, see this link: http://www.lowcarb.ca/tips/tips006.html