Over here on the wet side of the mountains, the MFG series has been allowing mountain bikes without fwd-facing bar-ends for all the years of its operation. I don't recall seeing a MTB rider on the podium all last season.
MFG isn't UCI regulated, so there's no 34mm tire max either. I recall a couple of jungle cross kinda courses where riders were rockin' 37 - 38mm tires and it may have helped on the comfort level, but not with their overall placement.