I don't know where you heard that, but it's not true.

I've replaced the u-joints on my front axle shafts on my 77 CJ7 twice. Each time, I pulled the shafts, and took them to a fairly large local auto parts store that does some machine shop work. I had them install new u-joints both times, and also dust shields one of those times.

After I reinstalled the axle shafts, I had no problem whatsoever with the wheel bearings. Of course, I cleaned out the hub and greased the wheel bearings and races like I should.

The hardest part of the job was getting the spindles off. They sort of get rusted in place and are a bugger to get off. The first time I did it, which was the first time they had been off since new (about 18 years), it took me about 2 hours of sweat to get the spindles off. The second time (about 8 years later), they came off pretty easily.

BTW, as long as you have the spindles off, you might as well replace the spindle bearings. As well as the axle seals.