^ I have often wondered what species Steve Buscemi is.
For that matter, it's possible that the Orions are not unified into one planetary or interplanetary state. Maybe there are two or more Orion polities, with one that's more Federation-friendly and another that's more hostile?
Any world that wishes to join the Federation must be unified into one state ("Attached"). So if Orion is not so unified, then it can't be a member. Also, even if Orion is a member, then its practice of slavery would also not allow it in, as that would surely be forbidden under Federation law.
And it's also possible that there's just a significant Orion diaspora within the Federation, with its members as citizens of the Federation and of whatever Federation Member State they live in. (Maybe there's a large community of Alpha Centauran Orions, or Ithenite Orions, or Grazerite Orions?)