They don't use bearings: you are right. However, I wouldn't build an ultimate wheel the way you are planning to. The stresses are much higher than JB Weld could cope with. All the weight, bending and torque reversals would break it in no time. A good unicycle is more heavily built than a bicycle, and a UW has no frame to distribute the rider's weight. I'd want a super strong wheel and a bomb-proof crankset. A bicycle hub axle is way too frail to put cranks on.