The Ural is a locked diff.
I would say that if there is no possible "difference", in shaft speeds, then it's not a differential, it's just an angle drive.
The Ural's driveshaft ends with the angle drive for the bike's rear wheel and the cross shaft driving the hack wheel is locked to this rear wheel at 1:1 when engaged or it's left unlocked and the hack wheel is not driven. If the cross shaft is engaged, and the bike is driven on a "no slip" surface, one can damage the cross drive or engagement mechanism. Anyway, semantics, ... we are both saying the same thing.
So one could tow with a Ural, same as with any three wheeler, on pavement this would be with the single driving wheel, but towing a trailer through mud and snow, it could be with 2 wheel drive.
The "best" location, for the braking scenario, depends on the braking force distribution relative to the location of the center of mass of the rig, which depends on the load. A lot of analysis could give you a better guess, but my gut says something like offset 30% of the distance from behind the tug wheel towards the hack wheel.
If you were driving the fully loaded hack with no trailer on a slippery surface and locked up the brakes, would the rig spin to the left or to the right? Ideally the trailer center of mass location, projected parallel to the direction of travel past the center of mass of the rig, would act to counter that rotation.
But I bet most folks choose hitch location so the overall rig looks right. As with any towing, it's always smart to slow down.
Sure sounds like a lot of fun!