It sounds a bit like wobbles. Though it would have to be a pretty severe case for him to be hardly able to walk at all. The heat in the front feet sound like navicular to me, though he doesn't have the typical navicular stance you would expect to see. I don't know a whole lot about EPM, as it doesn't generally occur in California, but is it possible that if he were imported, or went to an international show or race that he could have contacted it? I know that its not your decision what gets done with him, but if you could be there when the vet comes out, I think it would benefit you to learn as much as you can, ask the vet your own questions, and maybe you've seen something the owner hasn't, that can help in diagnosing whats wrong.