Can Dexter EZ-Lube axles be serviced as regular axles?

Yes, you can do a manual regrease, and yes, you can change the caps, although I don't see any reason to do so.

And IMO many of the issues with the EZ Lube system is caused by lousy parts, and ham-handed assembly of those parts. I have had no issues with mine, but after checking them out I found that many of the seal bearing surfaces were damaged. Luckily not badly or in such a position to cause grease leakage, but it was a near thing.