Races are a different story - in a race you actually do close roads (even if its a rolling enclosure it is technically closing the road) and control traffic at intersections. For that you definitely need permits. In a race as long as you are in the rolling enclosure you are not strictly bound to the rules of the road - you of course need to follow the instructions of the officals, but you don't have to stop at signals or stop signs if the lead car does not.

For an organized ride, if you are not closing roads then I'm not sure why any special permits would be required. There could be reasons beyond riding on the road that I don't know about, but if the riders are expected to follow all the regular traffic laws, then they aren't technically doing anything that they wouldn't be allowed to do on any day - there's just more of them.