So, to recap:
- Señor 105 originated in an Iris Wildthyme short story and has appeared in three other stories in her series, both before and after the start of his series. Series regulars Sheila and Rodrigo also debuted in Iris stories.
- Señor 105's series, The Periodic Adventures of Señor 105, encompassed an anthology and nine novellas before ending in 2014, and it featured not just the Señor, Sheila, and Rodrigo, but also many other DWU characters and concepts, including Iris Wildthyme, Panda, the Celestial Omnibus, Theo Possible, El Jefe, Litany Chromehurst, and the Venusians from Venusian Lullaby. (Hyspero is also referenced.)
- This isn't intended by the series' authors to be some kind of one-way connection: in a Faction Paradox novel by the author of a Señor 105 novella, a character has a vision of a scene with Rodrigo from a Señor 105 short story by another author. Even more directly, Señor 105 has appeared alongside the Fourth and Sixth Doctors in charity stories written by Señor 105 authors; obviously these stories aren't valid, but they clearly indicate that said authors see the Señor as existing in the same universe as the Doctor.
- These appearances can be said to be licensed with the same faith we have that anything published by Obverse Books is licensed, since they publish it (originally via their ebook-only imprint "Manleigh Books", hence the original confusion). However, just in case there's any confusion, you can buy the Señor 105 stories on the Obverse website and also here's confirmation from Obverse owner Stuart Douglas.
- Yes, the creator said on Facebook that the series probably isn't relevant to a Doctor Who Wiki, but he's also personally written (since-deleted) articles about it here; besides, there's no reason to think that he knows anything about the four little rules, so an opinion about whether it belongs on the wiki isn't an opinion about whether it's set in the universe. (See all of the above evidence.)
Am I missing anything? This debate has been open for literally five years; I think it's about time for us to wind it down and give Señor 105 the coverage it deserves.