Unfortunately, how he is treated is the norm and maybe a little better than the norm. I've seen barn workers who were given a "place" to live as part of their salary. It was an old, falling apart camper shell with no running water or electricity, they had to use the bathrooms in the barn and cooked on a camp stove.
I'd slip the guy as fat a tip as I could afford before I left, and I'd be trying to see if I could get him hooked up at another barn that might treat him a bit better.
Be very careful though, dollars to donuts, he's not legal.