I can't imagine anyone even thinking about taking a small dog or pet on a cruise ship. Can of worms would be a mild comparison--you take your small dog, then I can take my cat--then another can take their favorite Ferret.
And, if all you guys are getting away with taking your " small " pets, next time
I'll bring my prize winning goat! How about my monkey--- then someone brings a German Shepherd -- how about the kids pet--Donald the Duck to paddle around the pool with the kid---absurd sounding ?? You bet but that's a sample of how it would go.
As I said, I can't even imagine anyone even thinking about that.