The Ebonheart pact?
Seriously?
The Dunmer and the Argonians would never, EVER, EVER work with each other.
Sure they would. First, take this bit from the Pocket Guide to Empire.
In the chaos of the Second Era, banditry returned to Black Marsh in force. Slave traders from Morrowind were freer than ever to exploit their southern neighbor, and entire tribes of Argonians were dragged in chains to the Dunmer land. Former Imperial officials founded warlord dynasties which earned a reputation for tyranny even in that dark time.
So during this period the Argonians are being completely dominated by foreign influences. Imperial warlords lording over them, and a booming slave trade. Their entire society is in a weak state. They have no clear independent government, like the Organism that is founded later by the An-Xileel at the beginning of the Fourth Era. And sure, much of the population may hate Dunmer for their transgressions, but they're a population without any power. Next, take this bit from The Argonian Account:
Scotti introduced himself. "I'm a senior clerk in Lord Vanech's Building Commission in the Imperial City. My job was to come here to try to fix the problems with commerce, but I've lost my agenda, haven't met with any of my contacts, the Archeins of Gideon..."
"Pompous, assimiliated, slaver kleptocrats," a small lemon-colored Agaceph murmured with some feeling.
Its made clear in the account that the Archeins had traditionally held power in Argonia--they were the ruling class--and it makes sense that they would exist under the dominion of the Empire, and that they (or another group with similar policies) would have existed during the foreign-dominated Second Era. Every society has willing collaborators. Just like Queen Elisef of Skyrim and the Hlaalu of Morrowind and the Forebears of Hammerfell. One might even suspect that the "entire tribes" that were "dragged" into slavery were traditional and troublesome enemies to the ruling and influential Argonians of the time.
The thing everyone needs to remember is that, and I use caps lock for emphasis,
SOCIETIES ARE NOT MONOLITHIC. Also, Argonia is a region, not a nation. There is no centralized authority. And whether ruled by warlording Imperials or by their own fellow Argonians, you can solidly bet that formal relations between Argonia and Morrowind were at their
highest during this period of intense slavery. You could even say that, the more booming the slave trade is, the better relations between Morrowind and Argonia there are.
And the Nord-Dunmer alliance has so much precedent that I hope you don't even need me to explain that one.