There's never been a prohibition on thieves or assassins joining Outlander, it's just generally not a good choice because you lose hide.
And the unique race/class combos were made available so people have gone forward and requested them.
As for Voralia, she was part of an IMM-run character challenge where pre-made characters were handed out and players were given certain goals.
It's not like someone just rolled up Voralia and slipped it past.
She was a central player in the global situation revolving around the characters in the challenge.
I certainly don't have a problem with it.