There are very few certainties with shotguns, odd things can happen with any ammunition and in any shotgun. The instructor in a recent shotgun class I took talked about a student's slug being deflected by the bill of a baseball cap that had been placed on a 3-D target, for example. As I said, odd things can happen.
That said, given good hits I don't think many targets will be able to tell the difference. Personally I prefer to use Kent/Brenneke KO slugs for defensive applications, they are sort of a semi-wadcutter shape, made of a hard lead alloy with sharp shoulders and cut clean cookie-cutter holes. They have also proven quite accurate in every smoothbore shotgun barrel I've tried them in so far. And best of all, they are relatively inexpensive- less than $2 per box of five, on sale, and not much more than that at regular price.
hth,
lpl/nc