I am still planning on putting together a faction profile but I am too busy at the moment.
Well there's a few issues here.
Hethrir did attempt to forge alliances with the Deep Core Warlords, not just Zero Command.
There is nothing in Legends that contradicts and much that directly, or indirectly support such an alliance. Zero Command is the only one mentioned by name. I would argue that since Zero Command was only mentioned by name it probably was the most prominent and the other warlords mentioned are just small fry like Moff Foga Brill or nonentities like Grand Moff Gann.
If you want to argue that Hethrir was working with Greater Maldrood or Delvardus then
provide evidence for it.
By the time of Desann(who was working for Hethrir) launching his Empire Reborn offensive Harrsk was dead and Zero Command reunified into the Empire under Pellaeon.
Hethrir forged an alliance with Harrsk and then Harrsk died. That does not contradict that fact that there was an alliance.
Let's take the logic you use here and apply it to the Pentastar Alignment of Powers.
The PA was formed in 4 ABY.
Jerec was part of the PA and died 5 ABY.
Grand Moff Kaine died 11 ABY and the PA was annexed by the Imperial Remnant in 12 ABY.
Jerec was only a member of the PA for about a single year, possibly less before he died. Under your logic, since Jerec and his dark Jedi died years before Kaine and the end of the PA, they should not be included as heroes for the PA.
That Harrsk was only briefly associated with Hethrir I am not disputing. I am
only asserting that he was
briefly but
definitely associated with Hethrir. Much in the same was that Jerec was only briefly but definitely associated with the PA.
Further The Disciples of Ragnos were formed after Hethrir and the Empire Reborn movement were destroyed, so the time lines don't add up.
In my original post I already stated "No mention has been made of Tavion's cult being associated with Hethrir after Desann's defeat but the forces at her disposal lead me to suspect she had the backing of Hethrir- that massive fortress of Taspir III seems like it would be beyond the reach of a lowly failed apprentice to a dark side adept."
I already acknowledged there is nothing that states Tavion was working directly Hethrir at the time. But the fact remains that the bulk of her dark side force users were directly recruited from Hethrir's surviving reborn.
Here's how I suspect it went down: After Desann died Tavion was given his position within the Empire Reborn by Hethrir. All of the surviving Reborn would serve under her and she would serve Hethrir. When Hethrir died she already had the loyalty of the Reborn and struck out on her own.
I also find some similarities between Tavion's scheme and Hethrir's in the Crystal Star. Keep in mind that in the Crystal Star Hethrir's plan was to make sacrifices to Warru so the alien creature would bestow even greater dark side powers to Hethrir. Tavion took the Scepter of Ragnos and drained locations of their Force energy to resurrect Marka Ragnos.
This is all speculation but it is interesting to consider that maybe Tavion's plan was actually Hethrir's. If Warru wouldn't give Hethrir what he wanted, maybe Plan B was to resurrect Marka Ragnos and have him instruct him further in the dark side.
I find it amusing to think that Hethrir would have trusted an interdimensional vampiric slime being more than an ancient Sith Lord.
In game terms, I think it might be fun if Hethrir's faction were to capture Korriban they could recruit Marka Ragnos as a hero. Like how Greater Maldrood can recruit Moff Getelles and Admiral Larm upon capturing Antemeridian sector