From the pics it appears Hayden Hawks won and set the course record in the new Hoka One One Rocket X. He ran a great CR time and race!
And that is a fast shoe. Remember Hayden also has some serious 5k/10km speed from his NCAA days (and super high mileage weeks to boot). I don't know JFK50 course details exactly (haven't run it), but there is a pretty long stretch on the towpath (basically like a road) and then the finishing miles are on pavement. Only the AT section at the start (first 12-15 miles or so?) would be more technical and tricky in a "pure road shoe", but obviously it can be done.
I think they had really nice weather today too (basically no wind to slight tailwind perhaps at times...course does a "U-shape" so hard to say with the wind shift over time?)...maybe someone there can comment?). Also it appears it wasn't super freezing cold (temps in the 50s maybe?) so that was probably pretty nice. It also appears the lead pack (Men's race) paced themselves really well with not a crazy fast start on the AT section, but then Hayden really opened up in the second half (at least on Jim's previous CR split). I'm just going off info I've seen online as obviously I wasn't there though.
As far as carbon fiber plates helping in ultras, I can't see this working so well on single track trail ultras (with uneven and soft terrain or technical trails). But for sure for the road ultras and buffed out trails (like JFK50 mostly is). Also there is a big difference running low 6-min mile or high 5-min mile splits on a relatively flat and uniform surface vs the 7-9-min (or slower) splits usually seen in trail-mountain ultras.