Hi
Generally, a unfixed male is too driven by hormones to befriend any other rabbits. They will generally only be interested in humping or fighting. I don’t think another male would lessen the humping behaviour – rabbits don’t just direct their hormonal behaviours at rabbits of the opposite sex. And he would be more likely to fight with another male. When my unfixed male bunny got out with my fixed male, he still tried to hump him relentlessly. He didn’t ever do it with humans, so it’s not necessarily indicative of how he would behave with another rabbit, even if he doesn’t seem that hormonal with you.
Some bunnies do enjoy the companionship of another bunny living near but not with them. They can still see each other, and mirror each others behaviour, and after time might even start to lie along the fence next to each other etc.
However, you do need to be aware that it’s much more work for you. I’ve had bonded rabbits, and currently have three single rabbits while I try to bond them and it’s a bit of a nightmare. They have to be let out for extra running around time in rotation, there’s three times the hutch cleaning, and they all territorially poop around the room. Unfortunately when you have two unbonded bunnies, there’s a constant battle to mark territory with poop.
Honestly, I don’t know a lot about hamsters, but I cant imagine a hamster living near him would bring him any benefit at all. I honestly doubt he would notice. If he’s got on with cats before, is there a reason why you wouldn’t be interested in another cat? Of course, again, it depends on the cat’s personality too.
Cocoa, unfortunately rabbits can seriously injure guinea pigs with their big back paws, and can pass diseases on to them that rabbits are resistant to, but guinea pigs aren’t, so it’s not advised to keep them together.