If you don't see the testicles and look often (they can suck them up), then there is a very good chance he is neutered. Some vets and shelters will tattoo the rabbits in the right ear to show that they have been done.
You can try bonding him to an intact female, but there are no guarantees. It really does depend on the individal rabbits involved. Before Amelia was spayed (about 2 weeks ago), she was bonded to Korr who is neutered (they are back together now). While they did get along before she was done, she did want to breed and Korr didn't really appreciate those advances. Other than the humping, they got along really well. Since she was only spayed 2 weeks ago, she still has some hormones, so it will still take a little while to see if she really clams down in the humping department.
Go ahead and try bonding them, but be cautious about it. I would wait until you can confirm he is neutered to avoid any accidents.