Bungie origionally made the Oghre big giant pigs, and I assume they wanted to make them giants for the light or something before they took Trow for the light.
Well, as we all know, Oghre are giant piggie beasts, and Maul are smaller piggie beasts. This represents the fact that Maul are either weaker, smaller Oghre subspeicies like Neanderthals to us, or that they are young.
And how did they survive the war with the trow if they are smaller and weaker? We know that Bungie meant the Maul to be Oghre giants just slightly smaller than the Trow and Forest Giants (and later Myrk giants), but for some reason never did this.
We all know that the Trow enslaved ALL Oghre. Those that did not allow themsleves to be were killed. Even those would would be the Maul. Why? Because if they were so incapiable of working the iron mines, then SB would never have accepted them or wanted them in his army.
My theory explains all of this. Ok it implies in the Myth 3 manual and several other sources, including the Oghre flavour and Myth encyclopedia, that Oghre were essentially humans in giant pig form. They had many complex cultures living north, and perhaps one of these mighty city states, probabally the essential leading state of the Oghre, insulted the Trow, bringing Trow wrath on it. But because it was like Madrigal; capital of the Province, made up of several city states, all Oghre fought back. So all were enslaved.
Now imagine that when Connacht and Myrdred freed the mighty beasts, (btw they are kinda stinky in Myth 3; good vs Archers but thats about it) and they fought that great battle in the Red Bay or whatever it was, that large numbers desserted and surrendered. OR, because the Oghre never reached Rhi'Anon, that the Oghre there were never freed. Now the Trow saw the destruction and suffering their iron caused, they abandoned it, and because they had no need for the iron anymore, they let their remaining slaves and the prisoners of war return to their homeland.
The Trow, not wanting to appear weak, never told anyone about this. Of course if they planned to, a certian event made this hard. Well, then they were trapped in Iron so they really did not have the ability to deny it anyway, so I suppose they never NEEDED to say 'we beat them' so Myrdred just saved them from a LOT of embarrasment. Then, after they werte freed, they were isolated kinda from any scholars. Want to interview a trow? Well, you take a right after the ranks of Thrall, then head down throug the practcing Myrmidon until you find the Souless and Fetch destroying some unruly Ghol, and there should be a trow about 5,000 wight to the left. Oh and after the war they'd kinda kill you if you tried going into their lands. They already lost enough of their number.
Now suppose they went back to their old way of life, perhaps some barbarian Oghre started Hun-like tribes. These named themselves The Maul. They lived off raiding Oghre settlements and such. They were made up of the small, weak and realatively unevolved Oghre that were not sent to combat and did menial jobs like farm food under the rulership of the Trow (trow never ate, but their slaves did. Where do you think the food came from? These weak and stupid Oghre).
This Maul tribe-Oghre kingdom relationship can be described as the same as perhaps, a Myrk Giant-Myrk relationship, or better yet, a Bezerk-Warlock relationship. Warlocks are weak, rational geniuses while Bezerks are strong, irrational warriors. The Maul are weak, raiding Oghre while those living in the cities are strong, hard working Oghre. Being uneducated, they never learned magics and written language like their smarter brethren, and they only learned to use clubs.
Now, as we all know, Soulblighter lured them to go to war with promises of an easy victory over an unprepared foe. Why were they so willing? Were there not weak, unprepared foes there in the Blind Steppes? No. The Oghre cities were well defended against such raids, and so the Maul tribes were starving. So they thought "Well then, FREE FOOD!" So they went to war. (And oh on a different note; anyone else notice how as SOON as SB went on the defensive after The Wall, the Maul dissapeared. I assume because of the whole no-more-plunder situation going on.) So they were fed, strenghtened, and so spread over everywhere else to plunder some more.
This answers why the Oghre of Myth 3 and the Maul of Myth 2 are related, why noone knew that they were not exterminated, why the Maul are evil, and why they joined so readily (even the GHOL took more convincing methinks!)