Here’ the thing that people forget:
Yes, OTTBs generally are forward horses, but usually, they are broke horses with good ground manners. For the most part they understand hurry up and wait, they definitely understand galloping in a group, horses coming up behind, horses passing, horses bumping. They’re used to the track shed row, with a hundred things going on at once, cars, tractors, goats, music, noise etc.
Here’s what they don’t understand so well - bending and turning, soft passive contact, whoaing with the reins, a long stretchy cross country trot and jumping.
If a horse off the track has a good brain, is generally pretty brave, has good ground manners, can w/t/c both directions without drama, go on a loose rein and doesn’t have a big spook; reclaiming them as a fox hunter is fairly easy. You have to teach the whoa from reins, introduce hounds, teach them to cross water and teach them to jump, but that can be done fairly quickly if the brain is there.
I’ve never had an OTTB that didn’t learn to love hacking out pretty quickly. You’ve eliminated several question marks by saying he’ll be a staff horse, he won’t have to deal with being bumped or crowded or the field reversing.
So if you really like this horse and think he’s worth a try, why not?
Worst case scenario is that he’ll need more time and you’ll need to find another horse for next season, which could also be true of a lot of the other things you try.