Did your farrier tell you they were too short? Sometimes it looks worse than it really is. I see it with cracks, people call all concerned but it's generally not as bad as they think.
Not sure either oil will promote growth but it does help restore moisture, like most of the products you can buy.
Hoof supplements, in my opinion are not a "magic cure all" but do help some. But it's also one of those things where you get what you pay for.
What kind of pasture is he running on to wear down his hooves so much? Must be pretty rough to do that.
The only way I know to promote hoof growth would be to first get him in a smaller area that restricts alot of movement. Preferably a grass or sand surface. Then increase his feed, if on any. Not necessarily the amount but the quality. Add a hoof supplement if you like. Keep some type of conditioner on his hooves and get shoes on as soon as possible as they will keep the hoof from wearing down.
Good luck and let us know how it goes.
:tiphat: