If BO can legally get the dental/hoof/whatever done in lieu of owner getting them done, & legally charge owner, that's a splendid idea!
Yet, the problem remains that the owner doesn't care enough to voluntarily maintain the horse & give the horse a life. So, BO needs to do all within his/her power to demand that the owner get on track, or else re-home the horse.
I'm disappointed in not only the owner, but the BO. Hel-LO, you can't allow neglect/abuse at your barn!