I have been trying to work out how my now-death knight draenei might have gotten himself into the situation he is in. Here is what I have conjectured so far:
Previously, he was a jewelry maker with some relatively minor military experience on Draenor, mostly of the "Here, hold this axe and protect the settlement" variety -- not exactly formal training. After the Exodar crashed on Azeroth, he took up his trade again and that was pretty much it, though he did get asked to assist with teaching some of the draenei's new allies some of the techniques they had brought with them. Either way, he didn't really get involved very much with the events of the Burning Crusade.
However, when the Scourge reared its nefarious head, he felt called to sign up for the expedition to Northrend. As his unit was traversing the Dragonblight on the way to support the 7th Legion at Wintergarde Keep, they were overtaken and most of them killed. His body was scooped up and resurrected, etc. etc.
Now, the real question is: Was there enough time for him to be part of the Acherus death knights and be freed at the Battle for Light's Hope? As best as I have been able to determine, the answer would have been "no," since the Battle for Light's Hope took place before the first Alliance ship set said for Northrend at all, so unless he had reason to have been on the continent beforehand, no dice.
The other question is, did the Lich King then (presumably) continue raising death knights? With all these Alliance heroes streaming into his backyard, and given the Converted Heroes wandering around in Icecrown, I don't see why not. If this is what happened to Shaatnez, though, then when would he have been freed from the Lich King's hold? My thought was upon Arthas' death.
I was thinking that he was probably being trained in Naxxramas, then sent out on missions through Icecrown, and broke free in the brief period between when Arthas died and Bolvar took up the mantle.
Thoughts?
The only in-game evidence I've seen of Scourge being converted back to join the Ebon Blade occured with the Shadow Vault quests -- and none of them were death knights. I'm not sure how possible/widespread it would be.
I think there'd be plenty of time for a draenei to be converted. From what I gather, the death knights at Acherus were being trained towards the end of BC, and their joining their respective factions takes place between the Scourge Invasion event and the start of Wrath. So, any draenei who was in the Plaguelands around that time could have died and been risen, same as any other race.
The official timeline lists the time between vanilla and BC as only a year, but I've seen a lot of people disregard that, since... people were RPing for almost two years in real time while the expansion was out, and "squishing" all of that seems silly.
[A] Rethenn, Yuros, Varenas, Tobahn, Chojo
[H] Rethen, Garmok, Dorenthal, Jom, Luekalo, Springpiston
My DeviantART~
The other question is, did the Lich King then (presumably) continue raising death knights?
Yep! They're called the Host of Suffering. There's not much info on them aside from what little the quest text gives you, but they were basically just a Northrend Ebon Blade re-do, this time lead by Orbaz Bloodbane, the Death Knight that fled during the Light's Hope event.
I find it very plausible that plenty of higher scourge broke out of control in the brief period that there was no Lich King. In Warcraft III, it's essentially how the Forsaken came around- Arthas was weakened and they broke free, and Sylvanas rounded them all up under a banner. There's nothing said of what happened with the all the Scourge during his death there, but a few minutes of the whispers growing silent would likely be taken advantage of by stronger minds.
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Ah, see, this is what I get for not being able to stomach very much questing through Northrend on any character I have...which is, funnily, part of the reason I wanted Shaatnez to not have much experience in Northrend -- at least not that he could remember! I'll have to go do those quests, Oliver.
As a complete aside, funny thing on the Host of Suffering; if you look at the unnamed NPCs, none of them are draenei:
Of course, there are no human females or night elf females either, so obviously this list is in no way complete. (I also really like the armor recolor the Initiates wear!)
[A] Abhayaa, Neiba, Shaatnez, Tammar, and others. <The Keepers> | [H] Nebet, Naraia, Wormdrooler, and others. <The Rootshadow>