I think that safety critical systems need to deal with bad data anyway. Adding an extra level of redundancy makes sense.

Maybe you could have a lower power transponder style technology in addition. This would just broadcast an ID after a fixed amount of time in response to a request. This could be compared against radar,visual, and broadcast information to actively verify data. And critically it could be independent of the rest of the cars systems. Obviously that is not a solution, but it does add another layer of redundancy