I greases the drivetrain this weekend and zerks on the rear drive shaft were a pain to get to. Had to keep moving the truck inch by inch to get them to face just right so I could get to them with my grease gun.
Front one was a snap to do, since I could just rotate the shaft by hand into the right position.
Question is, would it be safe to chock front wheel, put stands under rear axle near the wheels and put the truck in neutral, so I could spin the rear shaft by hand to position zerks just right?

 

yup. that would be safe.

 

You could also get a flexible attachment for your grease-gun:

 

I have the gun pictured above with flex hose. Very easy to use and well worth the cost rather than having to jack the rig up.

 

I DO have the gun with the flex-hose. I still found it difficult to get to zerks on rear shaft unless they point more or less down.
Perhaps I just need more practice.. this was my first time