Camber isnt needed at the back for live/dead/torsion axle rears... the manufacturer already designed the suspension to have its own toe + camber as it compresses, so no need for alignment.
For example i'll take my AD resort, an AE86 and a Myvi.
1. If you ever see an AD resort or a B14 sentra and you look under the rear suspension, the shock absorbers are mounted at the edges of the rear axle at a very angled postion. Its designed so that when you take corners hard it compresses, but not upright, compresses to have camber... The springs is up and down only.
2. Its the same for a KE70 or AE86, look at the rear axle, 4 linkages in the front of the axle, and the rear the shocks are angled. IF im not mistaken, the different length of the linkages themselves play a role in toe. The rear absorbers are mounted in a very angled postion again like my nissan for camber.
3. Myvi's on the other hand, use a TORSION beam suspension. AGAIN if im not mistaken, when it compresses on one side the whole thing actually twists, if you dont really get what im talking about, imagine twisting a metal ruler sideways... Thats also probably why ultra racing's ARB's for myvi's have no connecting points in the middle, only at the edges of the axle... The ARB itself acts as an extra piece of metal to twist.
ALL of these theories, i've just thought over it for quite some time after research, so if im wrong dont kutuk me yaaaa... Thanks guys!!!