Scott Peck, a noted psychiatrist, wrote a book entitled PEOPLE of THE LIE. I don't recall if he believes they are BORN evil. Anyway, he posits the theory that there are people indeed who are simply evil--not just psychopaths, sociopaths, etc with horrid family background. He based this on his extensive work with such patients over the years. Some of the case histories will make our skin crawl. Scott Peck was not Catholic, although he worked closely with a Catholic priest and wrote of this in his final book regarding exorcisms. However, the former book is interesting regarding the subject your are asking about. I agree that God's grace and love is far greater than any evil and such people can truly repent and be save if they are sincere. Thus, such a repentance would be known to God and the person alone. Int his I'm thinking of prisoners who have committed heinous crimes, find God at the last minute and claim to be saved. It is between those epople and God to know the sincerity of the pardon of sin.
N.B. Peck is now deceased. Some of his ideas are not in line with Catholic thought, but his above mentioned book is worth checking out.
Pacem