With the injury gaping open like that, I would for sure recommend wrapping it. We had a gelding cut the back of his fetlock on the fence - deep enough to hit a small artery, but not deep enough to hit a tendon. He walked around spraying blood everywhere, but not limping. The limp came a bit later - guess it started getting sore.
Needless to say, we called the vet out. By the time the vet got there, we had pretty much stopped the bleeding. He cleaned the cut out good, and because of the location, advised against stitches. He did, however, recommend keeping the the whole hoof and lower leg wrapped to keep debris out of the wound.
We changed dressings every other day for almost two weeks before the vet said it might be safe to leave it open. We also used a powdered antibiotic the vet gave us in a puffer bottle. Horse healed up fine, but it sure was a lot of work.
Now - I have nothing against Underwoods at all - its great stuff. I used it on Rain when she stuck her foot somewhere it didn't belong and ripped the front of her fetlock open. Daughter was all panicked wanting to call the vet, but when I got home to see the injury for myself, I realized it looked bad, but was not deep. It healed up just fine with the Underwoods, and it sure was a lot less work than the gelding's cut was... but it was also a lot less serious.
Plain Old Dee, horses Dancer and Rain I believe in dragons, unicorns, good men and other mythical creatures!