Not every orc, goblin, or kobold is standing in a 10' by 10' room guarding a chest. If you have a living megadungoen in your campaign some of the occupants are going to have jobs beyond soldier, scavenger, or sword-fodder. Here's a list of suggestions:
Gong Farmer- all that “pure” has to go somewhere
Puppeteer- puppet shows are popular, “Punch and Punch” being a traditional show.
Fortune Teller- everyone is superstitious down in the deep dark and want to know what fate awaits them
Messenger- carry messages back and forth and often able tap-talkers,
Carpenter- wood working is of prime importance even deep in the earth
Miner/digger- ever busy opening up passages and spaces in the deep dark.
Dungeon Sweep- clean the chimneys and corridors of the dungeon
Cook- almost everyone has to eat and these are the pros that help there
Corpse Gatherer- bodies are in a ready supply and make traveling corridors difficult, when the lowlife cleaning crew is kept in check someone has the haul the bodies away, some serve necromancers, some supply university doctors on the surface, other supply cooks that aren’t’ choosy about the source of meat.
Crystal Husband- crystals have a host of industrial and magical uses and making sure they grow appropriately is a lucrative and skilled trade for the patient.
Drain Sop- someone has to make sure the dungeon doesn’t flood.
Mold Scraper- can safely clean and peddle a variety of mold, spores, and fungus
Websweep- dungeon sweeps that specialize in webs of all sorts.
Mason- dungeon engineers and master stone-workers
Trapsmith- build traps to keep their allies safe and keep foes away.
Locksmith- someone’s got to put locks in all those dungeon doors
Rat Catcher- rats are all over dungeons, they are trapped to remove the nuisance and provide food,
Spider Milker- collects spider venom.
Blacksmith- produce and maintain metal goods
Weaponeer- makes weapons of all sorts, skill and type will vary with race and culture of weaponeer
Armorer- makes armor in the dungeon, knows how to make armor form some exotic dungeon materials
Cobbler- if there are humanoids in a dungeon there are lot’s of feet in need of shoes
Porter- everything has to be carried.
Festergroom- fungus grower
Jellyherd- can motivate, even control a host of lowlife underground jellies and slimes.
Roottapper- know which roots to tap or harvest for a variety of products and means.
Rootchopper- lumberjacks of roots
Wormcharmer- understands worms and insects of all sorts and knows how to handle them
Roustabout or Whip- the labor force of a dungeon needs someone to keep it in check and working
Lamp-lighter- dungeons need light, and keeping those lights lit is the job of these chaps
Snail-herd- snail herders for food or other domestic use if they grow large enough.
Drink-bearer- carry water and much needed other drink throughout the dungeon.
Dark Cantor- entertainers, and news sources in the deep dark, underground bards.
Knocker- send signals throughout the dungeon by taptalk
Bump-tramp- the prostitutes of the dungeon
Lousepick- everyone in the dungeon suffers from lice and other infestations and when the itching is too much to bear they call upon the services of a lousepick to remedy the situation.
Spinners- make rope and other lines and weave cloth for other dungeon residents.
Peddler- see Peddlers of the Deep Dark http://aeonsnaugauries.blogspot.com/2011/03/peddlers-of-deep-dark.html
Limner- painters of the dungeon. Everyone doesn’t like them joyless and drab.
Turnkey- dungeon watchmen, keepers of keys, and jailors.
Torturer- torture is a common punishment and well developed craft of the dwellers in the dark and those with talent are always in demand
Pit Fighter- fight for fun and profit, sometimes in pits.
Man hunter- will travel to the surface to hunt men and other folk of the surface world.
Mummers- entertainers that preform short traditional works with dubious skill.