I don't think you have any business contacting his employer. The time to do that was before you hired him. Then you would have some pretext for calling employer now - for instance, if the employer had told you that this guy is very competent and reliable, you could report back that that is not the way you found him to be, and ask (rhetorically or otherwise) why the employer had approved of him. But in your situation ...

Obviously, not everyone would agree me. Just my opinion, as so many people say on the 'net.