Oils on the outside of the feet don't really do much.
As a farrier I always suggest increasing calcium, but fireweed is right. Your Ca/Ph balance needs to be right.
There was a study done in 1999 where they compared calcium and biotin. Only one horse had increased better hoof growth on biotin. The horses on calcium all had better growth, better quality feet.

Most hoof supplements have higher calcium, some have biotin as well.