I just thought of a tie-in with Southern Comfort & Hambly's "Ben January" stories that you might like:
The movie is full of swampland & the kinds of mantraps & ambushes you can set there...and of course, there is the hazard of gators & other predators. The books detail the daily life of the underclass. You could use Lizardmen or their equivalent to fill that Cajun trapper, slave & Alligator roles simultaneously.
(Kobolds could also be used, as could Gnolls, Goblins, or Orcs with the Reptilian template. Modified Kuo-Toa, Sahaugin, Locathah or other bipedal aquatic races might also work with some work.)
As sentients that are somewhat looked down upon by other races, they're ideal for the role of slaves/day laborers, working in the city by day, by night, living on the city's periphery, in "unwanted wastelands." Their underestimated intellects, natural cunning, and having swamps as a homeland make the bayous surrounding the city incredibly dangerous.
That way you REALLY capture some of the paranoia that the ruling class had at being surrounded by an underclass of servants who could rise up at any time...a society balanced precariously on the edge of upheaval.