Yes, I'm certain that the experiences of being expelled from a couple of schools and serving time in prison for credit card fraud have affected Stephen Fry's acting career. First, it's given him insight into areas of life not everyone gets to experience. Second, it's given him the chance to meet unusual people that he can tap into for reference when he's acting. It's good that he's overcome his troubled past and channeled his energy into acting instead.
I don't see how school explusion and jail time couldn't permanently affect his life. His acting career is in some way a reflection of his life, and I'm sure he draws on a variety of life experiences when he's performing. He also had a troubled childhood and adolescence, and those factors too should be considered when looking at the person he is now.
Stephen Fry overcame his rough start in life by earning a degree in English and pursuing his acting career with fervor. Some may argue that being expelled from two schools and spending three months in prison for credit card fraud gave him insight that helped his career, but that doesn't really answer the question. Fry is a great example of a person who turned his life around and went on to do very well, becoming a famous, award-winning actor.