I would have at least extended the grouping restriction to Tribunals. The idea being a unaligned person is "on the fence", so you shouldn't group with them until they come down one way or the other: either as an oath or as a member of an enemy cabal. But a Tribunal has already come down off the fence, so to speak, and joined a cabal that the Empire views as fulfilling a useful purpose. With a Tribunal there's no lurking suspicion in the back of the Imperial's mind that the guy is lying to him when he says he'll eventually take the Oath. You know the Tribunal never is, so you know you're not being deceived (in that particular way).