How much thread is the wheel nut engaging with? Considering the chunky integrated washer.
Not sure I'd trust the (lower) mount like that either. Too much weight might put too much pressure on that little bracket thing (mechanical advantage and all that, plus the weight is on the end of the bracket and not sitting over the axle). I'd be tempted to get a different fork with rack and/or mudguard eyelets. Shame its not a cup and cone hub or you could just get a longer axle and mount the rack after the wheel nuts (with more holding it on - or spacers to bring it out from the fork)