This is correct. The Gürzenich Orchestra is the resident orchestra of the Cologne Philharmonie and the resident orchestra of the Cologne Opera. The WDR Symphony Orchestra is also based in Cologne, but is - as the name indicates - the orchestra of the Westdeutscher Rundfunk (Radio Station of Western Germany) which itself is also located in Cologne.
It's nice to have the Gürzenich (wondering how that is being pronounced, anyone?
) back with a prestige recording project. It is a very fine orchestra boasting a dark and heavy sound, somewhat similar to the Berlin Staatskapelle or the Leipzig Gewandhaus Orchestra - which should suit Mahler's music naturally quite well.
I can say I'm looking forward to this cycle.