said by AndrewW:So I need to amend my initial question by requesting a list of Usenet providers who ignore DMCA takedown notices and cancel commands.
Cancel commands are really a non-issue to be honest. DMCA can affect any provider at any given time and none want to get the reputation that they "ignore" them. They may not get many or any, but as public discussions continue about them ignoring them...this information moves up the chain and does not go unnoticed.