Just be sure that he has been neutered correctly. I have a friend who had her boar neutered, had them seperated for a few weeks to be sure that the "plumbing" was completely clear.
The boar was very frisky when they were put together, but being a boar you kind of expect it sometimes. Unfortunately, about 3-4 months after having them together the sow was definately pregnant.
Turns out that somehow the vet botched the job up, and one testicle was still there and in fine working order!.
Thankfully the pregnancy went well, ended up keeping all the babies - housing the baby boars with dad, and the sows remained with mum.
Matt