I'm interested to learn the logic of this position.
From what I can tell, during normal operation, the "rear axle, bearings, and housing" have thousands of pounds on them (ie, the weight of the tractor, minus the weight of the rear tires/wheels/fluids). If you lift the rear of the tractor off of the ground, they instead have only the weight of the wheels/tires/fluid (pulling down, but the bearings don't care which direction the force is applied), which is considerably less.
I can see the bolts that attach the axle to the frame being stressed in an opposite direction than typical, but these forces are probably considerably less than they handle on a day to day basis when the tractor is being used as a traction device.