Sniffing the other's bum is a way for them to figure out if where the other bunny stands For example, If female, is she ready to mate, if male, is he displaying a dominant scent. HOWEVER, most of the time rabbits begin to smell the bum of the other right before they try to mount. Or they test out how the bunny will react prior to mounting - as sometimes mounting a bunny that doesn't want to be mounted can turn into a nasty fight.
That's why many bunnies will turn around and nip the sniffer! They are saying - "Don't even think about it! Buster!"
So though Scout was displaying submissive behavior, by sniffing Jhumpa rear, he may be trying to manipulate his way towards a mount - he may be testing out some dominance
You don't have an impossible situation, but you certainly have a huge challenge. First, like Gravehearted mentioned, both are males, which can be tough. Second, Scout is not neutered. Talk about male hormones - Even though Jhumpa is neutered, Scout's scent as an intact male, can deliver a territorial message that will make Jhumpa want to fight over territory.
Is there any way you can determine the sex. How old is Scout? His eh hem "jewels" should show soon.
If he's not old enough yet, then be very very careful when he reaches sexual maturity. A horrific nasty fight could break out when his hormones are in full force. And if they fight, rabbits can hold grudges!
Ultimately, the easiest way to bond is when every bunny has been altered.
Keep us updated!