Sort of yeah. If you have a bad chin it can be improved to an extent by stregthening the jaw and neck muscles but you will never have an iron chin.
Somepeople are born with a couple things that can give you an iron chin, one is a sightly thicker skull, like a 1/4" I believe. The other is an extra jaw muscle ( I was blessed with this one, makes it a real bitch when the dentist has to stick a needle in it, lol, he basically has to hammer it in and it hurts like hell.)
The biggest factor is seeing the shot coming and being able to brace for it as well as roll with it though. It doesn't take much to KO someone if they don't see it coming.