He's referring to the 'tulip' of the axle, the cup/outer race where the balls, cage and spider reside. When axles get noisy it's usually due to notches worn in the ball races of the tulip. The notches are normal wear areas, the balls predominantly ride in a small area, mostly straight ahead (within a few degrees.) That's why you normally hear a bad axle when you turn the wheels and accelerate - you're hearing the balls running in and out of the worn areas.
Some rebuilt axles are better than others. Some days a person feels like doing a good job, other days...
Who knows? I can't remember the last time I installed a new axle, the rebuilts are normally never a problem. However I never use locally rebuilts, I always install a national brand.
As far as accelerated wear due to lowering, well, hmmm... Lowering the car will increase the angle vertically at both joints, which will cause it to have a slightly wider 'normal' wear path. I'd say it would probably have an effect, but not one that should make enough difference to be concerned about. The axles I install never return for replacement, so I'd have to say they're probably good for at least an additional three+ years. Unfortunately I'm not installing near as many axles these days as I was, say, five years ago. Most everything on cars are sooo much better than they were just a few years ago.
Beav