I think the safety concerns are more around untested configuration (3rd party wheels) and in the land of lawyers, liability disclaimers. Is there risk, I'd say yes. How much added risk, negligible for crash absorption. But as others have said, could be significant on handling changes which in turn could result in an increase possibility of an accident as your vary from stock configurations. And this isn't always a negative, changes from stock could actually improve handling and thus enhance accident avoidance (stopping distance, grip, etc.).