Asmodeus = Ahriman?

I like the idea of a third serpent that Vecna talks to.
Rule-of-Threes and all that.

I don't think Ahriman and Ahrimanes are actually related, they're probably just two separate authors' go at the mythological being from Zoroastrian mythology.

The Pact Primeval is the one that makes the most sense in the Planescape and general D&D setting since as a general rule the powers did not create the Multiverse, they were either born from it or born from the beliefs of mortals, while the first powers were borne spontaneously during the Multiverse's creation (much in the same way as the Baernaloth's). At most, the powers are able to create races of beings, strongholds, or over a LONG period of time, a layer or level of a plane, or a demiplane. The creation cycle in the general D&D and Planescape cosmology is extremely complicated and a result of multiple variables. The Inner, Transitive, and Material planes are easy to trace because they were all born from the Ethereal (which contrary to On Hallowed Ground, would have been THE first plane since it is possibility and creation incarnate, and the Elemental planes lack the building blocks needed to create possibility-- not to mention that without possibility, the elemental planes could not be created.
The Outer Planes are much more difficult to define, and there were a lot of variables involved in their creation. It's likely however-- and certainly it is my view as seen in my Timeline topic, that the Protogenoi/primordial powers were responsible for creating the Outer Planes or at least parts of them, and before then they would have been a void or part of the Astral plane and the territory of the Draedens. This would be the perfect catalyst leading to the war between the primordial powers and the Draeden. This would have taken place before the existence of mortals.)

^^That's even more of a headache to think about than the effects of time travel.

There is also Ahrimanes Chief of the Cacodaemons, mentioned very briefly in the Appendix at the back of Fiendish Codex 1. I don't know if Ahrimanes is featured in any pure canon beyond this, but I tend to assume this to be a reference to Ahrimanes the fallen planetar featured in Green Ronin's Hordes of Gehenna.
I don't know what a Cacodaemon is in D&D (but if my players ever visit Ahriman-abad they are likely to encounter cyclopic pumpkin monsters that spit explosive gas balls)
I do not recall if the Cacodemons feature in 1E, but in Necromancer Games's stuff (such as City of Brass), they are indeed a type of Yugoloth, it appears as an all-black, bald humanoid.
Even beyond that, if you take the original Greco-Roman myth into account, the Cacodemons (unless you decide to make them their own separate species) fit most closely with the old-fashioned/Gray Waste style Yugoloths, as in Greco-Roman mythology, they are spirits/personifications of the negative things unleashed from Pandora's box-- many of which are not sins per say-- things like pestilence, insanity, toil, battle confusion, old age, famine, curses, pain, helplessness, nightmares, etc, in addition to sins. Also, in Greco-Roman myth, the vast majority of them (Phobos and Deimos aka panic and dread being among the exceptions) are children of Nyx or Eris (Eris herself is a cacodemon), who are Protogenoi (the first class of gods which were viewed more as abstract personifications such as ocean, mountains, darkness, creation, etc. rather than anthropomorphic beings-- in D&D terms they would be elemental beings) If one were to encorporate this into D&D, it could result in some VERY interesting relationships between the Yugoloths and Nyx and Eris, since, for one thing, Charon is supposedly one of Nyx's children. It might also raise a question as to whether Nyx and Eris have slowly turned themselves into Yugoloths in a similar vein that Pazuzu has turned himself from an Obyrith into a Tanar'ri (and might explain why Nyx and Eris are depicted as anthropomorphic beings unlike, say-- Erebus and Styx) Perhaps secretly, Nyx played a role in the creation of the Yugoloths-- maybe she or one of her aspects is also in fact a Baernaloth-- now that would be quite interesting. (it's worth noting that Nyx and Erebus are both considered part of the Cthonoi, aka the underworld gods, and originally all the cacodemons were as well. Though Eris, Phobos, and Deimos are considered part of the Ouroi along with Ares-- that is, the sky gods.)

Nyx is mostly independent of Hades, though. She's one of the Cthonioi, but she doesn't answer to him... or ANYONE.
Also, I'm not sure that Hades has much interaction with the 'Loths-- Hecate probably does, however (and the hags, too). Hades aside from the kidnapping of Persephone is pretty True Neutral and Kelemvor-like (though much more apathetic). His primary concern is maintaining the balance between death and birth/creation. Hecate is a bit different, but still under his command, and for the most part she obeys his rules. She controls armies of ghosts and demons, but the ghosts are already bound to Hades and are simply gated to the Prime on certain nights. Neither Hecate nor Hades could possibly be Baernaloths, as neither is old enough. Same goes for Annwan and Hel.

I am well aware that Charon is an arch-yugoloth in the canon. Hence part of the reason I suggested that Nyx might secretly be one of the Baernaloths (she wouldn't be the one responsible for creating the General of Gehenna however)