It is rare that an exit node is raided but there has been no known occurrence in which a normal relay was raided.. nor would it make any sense for there to be. Many people run non-exit relays as they are uncomfortable with the risk of exiting for the Tor network, perhaps you should be one of them.

For exit nodes, the issue of legal liability for routing other's traffic is less clear. You'd basically run the same risks as providing an open wireless network: https://openwireless.org/myths-legal