Cheating is the word for it if everyone's expected to carry stipulated gear - whether it's FRA policy or at the stipulation of the RO. I've seen people DQ'd on the OMM for failing a finish-line kit check and full kit is something that's adhered too.
Whatever the safety aspects, surely the ethos of fellrunning is such that a level playing field and sportsmanship are still values that we all aspire too when we enter a race?