Thanx,
Sthelysh
If they're hiding, they're not doing a very good job, since their appearance and species are well known in Sigil.
Although there are rumors that one or both of Sigil's two famous arcanaloths might be exiles of some sort, yugoloths usually don't do that. They expect betrayal from one another as a matter of course. They'r'e not beings of law, after all, and strict obedience isn't required of their kind. If a 'loth is behaving in accordance with his/her evil nature, the schemes of the 'loths are assumed to be in capable hands. And betrayal is part of their nature, so this is even encouraged; the master plans of the General of Gehenna take this trait into account.
If A'kin has truly turned his back on evil, however, that's true treachery, and he cannot be allowed to live. He would be persecuted with the same fury that Apomps is, and he would not dare leave Sigil. Of course, as far as anyone knows, he doesn't.
Nothing short of abandoning the yugoloth race and adopting the goals of another would merit true exile. Apomps, who betrayed the plans of the other baernaloths by creating a seperate race with their own destiny, is one such exile, and if he were not a god, or almost one, he wouldn't have survived this long. A 'loth who completely defected to the tanar'ri and baatezu might also receive the final punishment.
Similarly, some claim that the Marauder is likewise the personal representative in Sigil of either the Oinoloth or Khin-Oin in general. However there's no -known- evidence that she answers to any superior besides her own fickle whims. This might explain some of the animosity between herself and the friendly fiend, or they might be professional rivals, former lovers, brother and sister, mother and son, father and daughter, or some combination of the above with the animosity a complete act in public. Or the truth might be stranger still. Who knows
It's like a lower planar good cop / bad cop...
If she and he are working in true form for their race's goals than they should have access to the Tower's collective knowledge. If either is a political exile of any sort from the normal heirarchy (even if they're still evil) they'd likely be stripped of the power (which happened to an Arcanaloth in Carceri in the 'Well of Worlds' module, he was still evil but had fallen into political disfavor and was stripped of every bit of his sorcerous ability). Of course if they would have hidden this fact utterly in true 'lothy form.
Or the truth might be stranger still. Who knows
It could, for instance, be that Shemeska is the good-aligned one (or suspected by the other 'loths to be) and A'kin is supposed to monitor her in case she shows signs of it.
Of course, you didn't hear that from me...
“You were selling mercenary service to the Ysgardians?” Dai Khulus raised an eyebrow in surprise.
“No, a cambion. He was leading some kind of invasion there. That didn’t go well, I hear. I don’t care. The deal collapsed when A’kin vanished.”
“You were in Khin-Oin at the time?”
“No, no. We were at the Tower Arcane. My brother A’kin’s official title there was the Shopkeeper. He was the public face in most dealings there. When powerful pit fiends and balors came to the arcanaloths to purchase yugoloth mercenaries, it was A’kin’s smiling, cheerful face they met. They called him the Friendly Fiend, you know. I worked under him then, but when A’kin left I lost my job too.”
“How did your brother become involved with the politics of Khin-Oin?”
“We were always involved. That’s how we earned our surname: a’Khin, originally, inherited from our predecessor. Yugoloths here knew to call in the A’kins whenever heavy lifting needed doing.”