Personally, I'd have a talk with the guy. I'd inform him about what I had learned, and that I was concerned. I'd ask him straight out if he can work professionally with Jews or other minorities. If he can't give a clear, positive answer to that, I would have to let him go, since he wouldn't be able to do his job.
Furthermore, I'd inform him that because of his political views I would find it impossible to let him be the supervisor of any employee who is a minority or otherwise not accepted by him. Not only would I find it hard to trust his judgment of them, but the company could easily get sued by disgruntled employees. This will of couse make it very difficult for him to advance in the company.
If I otherwise trust the guy, and he still wishes to continue working there, I let him stay on. But I'd still feel the need to keep an extra eye on him from now on, so I'm not quite sure how long that situation would be tolerable for either of us.