i have a decent six pack and i work it out no more than once a week. at no point in my life have i ever worked my abs every day to get said six pack either, since what i eat makes my abs. working it out just helps me shape it and makes it sort of get bigger.
if you are asking if you can physically work out your abs everyday? yea i guess, why not, except you might over train it, and/or not get any gains from it, and ultimately just waste your time. if you're correctly doing core exercises, you should not need to work out the abs more than once a week.
my typical routine, usually after running a couple of miles:
3 x 10 decline sit up with 25 lb weight
3 x 10 crunch machine with 85 lb resistance/weights
3 x 10 hanging leg lifts (while doing pull ups)