Yes, Vetericyn (spelled correctly that time) would be the BEST thing for that injury. Shoot its the best thing for ANY injury in my opinion! I am a firm believer in that stuff :) I mean take a look at what it did for my mare.
She got caught up on a bolt after what we think happened because another horse started kicking at her while she had her head hanging over the fence with the gate (gate bolt) to her left. The bolt stabbed into her and she got hung up. After trying to pull free the damage was a ripped open gash that was about 8 inches long and 8 inches deep, she also had puncture wounds under the skin that you can not see from the bolt that were about 6 inches deep and full of air (because of these the vet stitched her up). My mare ripped her stitches out about two days later and the vet told me to just leave it opened and keep it clean. So that is all I did, other then adding a few squirts of Vetericyn :) the 3rd picture is of her injury only about 2 weeks later and the last picture is of the scar it left (she does have a little bit of a winter coat in this picture).
I think it will help loads with your horses injury but just know that will an injury like that, that actually cut the coronet band, it will most likely cause your horse to have a split/crack straight down and all the way through his hoof. Nothing that should cause him any pain or prevent you from riding him, it will just look ugly. A friend of mine owns a gelding who injured his coronet band when he was very young and it caused a straight crack down his hoof, because the coronet band is forever damaged. He runs barrels and has no issues, she does shoe him during heavy show season just to prevent extra stress to the crack but she has had no issues with it.
p.s. Before anyone says anything about the bolt just know that this was not on my property (she was staying over at one of my friends places for a night because I was visiting with them) and the bolt was cut off shortly after.