Changelings would probably think ethics were merely some notion of the solids. You could almost say changelings were a scourge of the galaxy for they simply detested all humanoids (before Odo came along that is and told them otherwise) and the solids were pawns to be used where necessary. I mean every enemy of the Federation could be reasoned with (aside from the Borg): Klingons, Romulans and so forth.
Not so with the changelings, it was either submit to their will or be enslaved or annihilated, there was no middle ground. Even more disturbing the changelings seemed to admire animals more than humanoids, I guess the changelings thought the humanoids were parasites of the galaxy, causing ecological damage and interfering with the natural order of things.
Do the changeligns have ethics? Perhaps but they have probably forgotten about them given their Great Link is the equivalent of Nirvana or a utopia. In a perfect world there is no such thing as right or wrong, thus the changelings shun everyone else who can not join (the solids), for such races would cause imperfection to the changeling way of life.