I had a vasectomy aprox 10years ago, and have been in a relationship with my girlfriend for the last three years. She has not been on the pill or any form of birth control for the last two of the three years. We have had no issues up until most recently when her doctor requested a pregnancy test based on the short time between her last period as well as some additional concerns, it raised a concern in my head..
What is the percentage of chance for me actually producing active sperm?

While it is possible, the chances are very slim. A vasectomy for men, and a tubal ligation for women, is the most effective form of birth control.

With a vasectomy, there has to be at least 12 ejaculations between the time of the vasectomy and the first intercourse to be sperm free, so to speak.