Long Live the Confederation!
Only thing that comes to mind as to why the Hellcat and Longbow were in WCA aside from the producers feeling that the wc3 ships looked cooler and thought maybe the "kids" wanted to see them.
This is how rumors get started. It doesn't really make sense - the Wing Commander III and IV ships are all fun cameos, with the possible exception of the Hellcat (since it opens the series.) You see the Avenger, Longbow, Arrow, etc. for a few frames each...
Rather, the show should be praised for being the rare mass media spinoff that actually did go all the way back to the less familiar original game and use its ships.