No. The whole reason for not using juice with preservatives pre-fermentation is inhibiting yeast growth. If it's already done and you plan on just back-sweetening and keg carbing, using a juice or juice concentrate with preservatives like sorbate is just fine.
Now bottle carbing... That's a different story. I've never dabbled with that beast before (I'm spoiled and bought myself kegging equipment before anything else when I got into brewing) but there are plenty of other members that have it down to a science and would be great help.