It would be the Wild Nokotas, Fighting Nokotas or some other appropriate adjective. The intention wasn't to create a rhyming name.
I think over time, the nickname would be naturally shortened to "Nokes," just as the Maryland Terrapins are the "Terps," the South Dakota State Jackrabbits are the "Jacks," the Nebraska-Omaha Mavericks are the "Mavs" and the South Dakota Coyotes are the "Yotes." There are probably many other examples people could cite.
The Nokota horse breed is known for its intellegence, speed, endurance, strength and ability to survive harsh conditions. It is unique to North Dakota, which is why it's the official state horse. I can't think of a better symbol for UND's athletic teams.