I agree with those who have said that you may also need a new Vet. if this is the farrier your Vet recommends, maybe after seeing this the Vet will change his or her mind. If not, if your Vet thinks this is acceptable, then IMO, you will need a new Vet too.
What are of the country are you in? Mentioning that may get some more helpful tips on whom to call.
You definitely need to have the Vet see this horse ASAP, keep him confined, and you may even want to bed his stall deep so he can lie down to take weight off of that cracking hoof. If you have a large Telfa pad, after cleaning the crack area from all shavings, manure etc, put that pad on it, then use duct tape around the hoof, not just to keep pad on, but to offer some support to the hoof wall. Be careful not to get the duct tape on any hair.
If your Vet is any good, I would expect the treatment would be remove shoes, use the styrofoam protocol, and possible hoof cinch or more duct tape to help stabilize that hoof wall. I am not a Vet, nor a farrier, but as others who have posted, I have learned a lot from those who are experts in those fields.
Good luck, and keep us posted.