Welcome to the Daily Puppy Rucus and his Mum, from Oliver & Henry, and their Mum, in London, Ontario.
Tracy, to answer your question about how a JRT would "get jiggy" with a Rottie, I would think the only way possible would be for the coupling of a female Rottie and a male JRT.
I also agree that it is highly unlikely that is the pairing that occurred with cute Rucus, but only time will tell. It's going to be fun watching him grow and seeing him develop.
Neutering prior to six months isn't necessary, and it is better to wait. Shelters like to neuter as soon as is physically possible to be sure that no further procreation will occur.
It's lovely to see a picture of Mum and pup! Keep the pictures coming.