Don I respect your opinion but I do not see that in ULs own book.
All metal fittings for metal cable, conduit and tubing are considered suitable for grounding for use
I have never seen anything that says chase nipples must be used with locknuts.
The link you provided says that one application is:
To couple boxes back-to-back.
That would only place a locknut in contact with one enclosure.
The way I read 250.12 a locknut would be the "fitting designed so as to make such removal unnecessary"
If there is no locknut as on one side of a chase nipple, then paint removal becomes necessary.
Truthfully IMHO, it is a stretch to believe that the contact made between the straight cut threads of the chase nipple and a coupling, if made up wrench tight, would not provide an equal or better fault path as a die cast set screw EMT connector or coupling.
The only exception I would make to that statement would be for service conductors and the code requires bonding of all raceways in that application.