What you should do is allow him to hump her as long as she isn’t getting angry, and she isn’t being prevented from eating, and drinking.  He’ll stop once he feels satisfied she understands he’s the boss, and since she does seem to allow him to hump her for a bit, then it should be short lived (keep fingers crossed)  

If he becomes relentless, then you will need to give her a break, but still allow him to hump her in short intervals.  Let him hump for 20 seconds, comfort her while he’s doing this by petting her, and then push him off for two minutes, and let him repeat.  Then if you need to separate overnight or while you are away, then that is the last resort, but make sure that they still see each other everyday.  You don’t want to have to go through a rebonding process.

If you are still concerned about whether he’s intact then take a look:   You can easily SEE if a male has been neutered.  When a male is intact, it’s obvious if you know what I mean.  If he’s over 4 months, their testicles drop.   Though some males testicles can be pulled up, by now you would have most likely noticed them at some point..  If you are still not sure, then bring him to your vet.

It’s also funny when Jack tries to get fresh with Rucy.  All my bunnies are altered, but like you said, every once while, he’ll just try and see what happens.  Of course Rucy will have none of it, and he quickly gives up. 

But you can see hope in his eyes as they are grooming each other,  he gets “that look” and cautiously and carefully makes his way around, starts to make a move, and then Rucy runs away, and his hopes are dashed.  Sometimes he’ll follow her, hoping his persistance will pay off, but most times he just sadly watches as she walks away.