The raisins are very good for the cider. They provide the nutrients that the yeast needs to stay healthy during the fermentation process. I usually add a commercial natural yeast nutrient to everything I brew. Add the raisins when you pitch the yeast in the primary fermentation.
The Cider I started yesterday is really bubbling away this morning. Very active bubbles rising rapidly up through the cider. The yeasties are very happy! Not violent but very, very pleasing to see. The airlock is bubbling 37 times per min. or about every 1.6 seconds. Nice action!