Based on what I see here (Forged center section) they appear to be a good joint. Not sure why the "sealed" is considered advantageous though. I would rather have the grease fitting.

BTW--its good practice to install the fitting (or in the case the 'bump' where the fitting would normally be) in COMPRESSION. Meaning align it so that under power the driving yoke is squeezing it between the driven yoke, rather than trying to rip it apart. Use your fingers like a set of yokes and you'll get what i mean. The weakest part of the center section is where the fitting is located.
No its not LIKELY to ever fail, but this removes it from the equation.
http://www.duralastparts.com/gold.php?page=ujoints