Hiring someone for free?

I'm having my wedding soon. Now I found someone who is providing his services for free because he wants to use them commercially as part of his website. Now, by law, am I able to hire him for free, as long as we have a contract that says so? Or if someone works, I'm obligated to pay him because of some labor law? I'm not trying to be cheap but I figure hey, if this guy is going to post it on his site, he's gonna try his best. And also, with cost of weddings these days, I'll try to save wherever I can.