this has been discussed many times before. in this age of litigation, nitto has always been conservative with their weight ratings, but we're all adults and have to make our own decisions. that said, and keep in mind this comes from someone thats been running a nitto mini front for over 10 years with a basket, you can get away with more weight. now even i would say, if your plan is to bring back 15-20 lbs of whatever often, then thats not a good idea (imo), but for occasional heavy loads, its fine.
my bigger issue with this combo is i think the smaller racks are not wide enough of a platform for stability to secure a basket. i recently switched to a nitto/simworks obento rack and its been a little more stable.
you don't mention what bike you are planning for this, but if its a rivendell, most of them do not steer well with a heavy front load, which is another reason to keep it light.