Secrets in Smoke by Ashe Moon

Thomas is the captain of the Watch, a rank reserved for only the strongest human alphas. But he holds a deep secret: He’s an omega. When he’s forced to partner up with his rival and number one nuisance, the dragon firefighter Rainor, Thomas struggles to keep his natural scent hidden from the alpha’s sharp senses.
Rainor has never had much respect for the humans—especially Thomas, whose men can never seem to keep the town safe without the help of him and his dragon flight brothers. If he’s to teach Thomas the art of firefighting they’re going to have to break down some walls—even if that means exposing sides of themselves they’ve never revealed to anyone else. But Rainor quickly learns there’s far more to this human “alpha” than meets the eye—and nose! Can he keep it a secret?