The Dunmer are on the ropes, they have little choice, going to war with the Nords would destroy them. The Argonians are occupying Morrowind, they want it back.
I'd imagine much of their old pride is now gone (having your Gods disappear, much of your homeland destroyed and the rest being conquered by former slaves will do that to a people).
Plus, the Nords gave them warships (as detailed in the OP). An alliance with the Altmer or Bosmer would do no good against the Argonians or Nords. They don't even share a border.
I think it's perfectly possible the Dunmer would do these things.
I'd also like to point out that when the Empire invaded that a large portion of the Dunmeri people committed suicide because they would rather die than be under the rule of the imperials. The Aldmeri Dominion is a very powerful force that once it gets going could easily crush most resistance. I understand what you mean about not sharing a border, but seeking alliances with the Nords would just cause internal problems due to their past relations. I know for a fact that the Redoran, Indoril, and Telvanni would never seek alliances with the Imperials or Nords. And the Indoril and Redoran are practically the entire Dunmeri military.
I dont think the Dunmer would get so soft so quickly, they've always been an enduring people. They were cursed by their old god, had their savior killed, been at war for hundreds of years, and the whole time they never once got soft because something bad happened to them. Also just House Redoran alone held off the Imperial legions for 100 years, I think they could manage with holding off the Nords until they could form proper alliances with the Dominion. The Altmer have Sunbirds which are flying juggernauts of destruction as well as extremely powerful mages. Redoran soldiers supplemented with Altmeri mages and Altmeri Sunbirds would be an almost unstoppable force.
But like I said, that's just my opinion.
EDIT: Also I think the Argonians only took Southern Morrowind. I'm pretty sure that Northeastern and Northwestern Morrowind are still controlled by the Dunmer. Northeastern being the Telvanni and Northwestern being the Redoran. However it's been a while since I read that piece of crap book they put out there.
EDIT2: Here's my char sheet if I ever do decide to take a role in this. It's an old sheet that I edited a little bit, might edit it some more later on. There are a few things I dont like about it, but it'll do for now.
Spoiler Name: Thaden Andrethi, Hortator of the Dunmeri Empire.
Race: Dunmer
Age: 241 (Appears mid 30’s due to magick)
Gender: Male
Birthsign: The Warrior
Appearance: Thaden stands around 6’3” and weighs in at nearly 220lbs, he is muscular and very fit do to his rigorous training. His face is strong and well defined bearing a few scars the most notable stretching from his right cheek down across his mouth and to his chin. His head is shaven and doesn’t even bare a single stubble of hair. He has a twisting blue tattoo on the right side of his face as well, that covers the area from his brow down across his cheek. His eyes like all Dunmer’s are crimson red.
Skills: Through years of Rigorous training Thaden has become a master of bladed weapons as well as the use of destruction and alteration magick. He also feels very comfortable wearing native medium armors and other armors of similar make. Thaden is also extremely athletic and has a rather high endurance that allows him to keep going when others would have failed. Thaden is a warrior through and through.
Minor abilities: Thaden a natural leader and a master of rhetoric. He is also surprisingly adept at being able to survive in harsh conditions. His mental willpower is very high along with his overall intelligence. Thaden is also a master at war tactics and strategies.
Armor/Clothing: Thaden wears the traditional Crimson Armor of the Royal Guard, however his is beaten and marred with the scars of war. He also owns a rather intricate set of Gah-Julan bonemold armor, however he only wears it during some occasions.
Weapons: Thaden carries an enchanted Ebony longsword. When the wielder of the blade channels a small amount of magicka into it the edge of the blade will heat up to an extremely high temperature. The heat is enough to melt through thin metal armors or chainmail however it takes a bit more force to make it cut through plate mail armors. Thaden also carries a large razor sharp steel dagger on his belt.
Background: Thaden was enlisted in the academy at a young age by his father who was also a Royal Guard. The training program implemented at the academy is similar to how the Spartans conducted their militaristic society, only the strong make it out alive. By the time he was in his late teens Thaden had already been marked as top in his age group. Through many years of rigorous training and education Thaden had become the ideal Royal Guard, strong, smart, and deadly. At the age of 32 he was enlisted as a full member of the Royal Guard. He served the various Kings of Morrowind all the way up to the current King Helseth. During King Llethan’s reign he was promoted to captain of the Royal Guard. He served Llethan until his unfortunate and mysterious death. When King Helseth took over he appointed Thaden as captain of his “behind the scenes” Royal Guards, the ones that made sure everything went his way. During his time acting as a covert agent for Helseth he earned a reputation as a ruthless and lethal fighter, there is a rumor among the guards that he fought off over 2 dozen savage goblins in the sewers beneath the Palace while the other guards retreated back to safety. He emerged battered and wounded but alive. However during the recent events and the fall of the empire Thaden noticed the flaws in Helseth’s reign and renounced his allegiance to the Helseth and the old Imperial government. Even though he had served them loyally for many years he never had a love for the Imperialistic government and served only to benefit his nation. After the fall of the Ministry and the Invasion of the Argonians Thaden was elected Hortator of the Dunmeri Empire and is now the chief commander of the nation’s military actions. He has also restored his allegiance to the Great House of his families lineage, House Redoran.
Metal Description: Thaden is a battle hardened warrior, through the rigorous and intense training he went through as a child he was taught to ignore fear and pain. His mentality can be described as quick thinking, intelligent and decisive as well as ruthless. Thaden can become quite infuriated at times, especially when dealing with things that involve the Dunmeri people. He also has a passionate hate for the Imperials , Nords, and the beast races. He often refers to them as inferior races.