Don, I agree with your answer, but not the reasoning.
John I do not understand.
Welding cable is not (generally) listed as building wire.
If it is not listed in article 400 we can not use it.
The portable power cables we can use are listed in 400 and I think it goes without saying that you must use the proper terminals.
As far as I know the proper terminals are compression terminals, I don't think any lug that the set screw contacts the fine strands is listed for that use.
