Pasteurizing is done for commercial ciders, juices, milk to kill harmful bacteria, but it also kills good bacteria (or in this case, yeast) in the process. Some people like to use unpasteurized cider and let the wild yeast...run wild to ferment the cider. This can be either good or bad, and not so much as a safety issue, but a taste issue. Using wild yeast produces unpredictable results, as opposed to using pasteurized cider and adding the yeast of your choosing. I do want to try the same approach you are doing someday, but I have limited experience and played it safe with the pasteurized cider and adding yeast. As far as harmful bacteria is concerned, this comes in to play more with not having everything sterile before beginning your cider (carboy/fermentation bucket, any other utensils you used, airlocks, rubber stoppers, etc....) than using unpasteurized cider. Not that having some sort of tainted cider is impossible, but as long as your cider starts to ferment and nothing unusual is taking place, then I think you are fine.
