I've heard two versions of the union story that prevented code shares in Belfast before. One says no more than 2 destinations per airline (there are some airlines that have more, but they're all part of the AF/KL group); the other says no more than one code share airline per country ex Amsterdam.
Whichever is true still applies as EI offer ORK and DUB and FlyBe have codeshares from Amsterdam to UK destinations.