As the Prime is self powered, is it compatible for use with iThingies with the camera connection kit?
It's not self powered, in that the USB part needs power from the USB bus.
I think we need a more concrete example.
Prime + USB Hub + Camera kit + iPad
Would probably work
Prime + Prime PSU (USB connection) + Camera Kit+ iPad
Also
But that's only an informed guess.
In second case I suppose there would be two cables from Prime PSU. One the USB from camera kit through Prime PSU USB power pass-through to Prime USB input. And one from Prime PSU to Prime power socket.