I sailed on the Princess Diamond last year. I saw nice variations of bluejeans (with nice shirts, etc.) being worn at dinner. I did not see anyone turned away; neither did I see anyone come into the diningroom with worn looking blujeans.
I am planning on wearing a new pair of demin-looking Capris to dinner with a gorgeous top and shoes! I don't think this should pose a problem. Don't feel it falls under the heading of bluejeans.
If anyone disagrees with me, please advise. Thanks!