I assume they are both altered? What does the other bunny do when its mounted?

Mounting is normal, it's how they express dominance. Let it happen, then gently move the humping bun off the other so the other doesn't get too annoyed or stressed. If it is causing fights, end the sessions before it gets to that point, and do another session later in the day after a break.

They are both altered.
The bunny who is getting humped does not react much. She just tries to hop away and goes back to him a few minutes later to groom him like nothing ever happened.

If that is the case, it's going fine.

It sounds fine to me!

My female humps but my male would get very upset by it. If the humpee doesn't mind, it's really not a problem and they'll work things out.

Okay great! I just don't want to let them be together without me there until it gets a little more under control. I always get scared my humper will hurt the humpee. He usually takes out some fur when he mounts

Taking a mouthful of fur is normal and doesn't hurt. I think the biggest thing to worry about is the humpee getting upset with it and retaliating or become afraid. As long as the humpee is ok with it there's no problem.