There's a little discussion on cauldrons, sieges, and ladders; so will our dwarves get to make use of the former? Thoughts include pouring boiling oil over siegers climbing up on ladders (building it and loading it as a siege weapon)
Liquids are items, rather than flowing fluids, right now. Unless oil is implemented as an actual fluid, like magma or water, which is completely unlikely, then it could only be dropped as a projectile.
As in,
"The spinning cooking oil [5] hits the goblin in the left ear, tearing the skin and bruising the fat!"
So... probably not.
I was the one that posted the cauldron thread, and my original idea was more along the lines of spreading contaminants... for instance, a creature caught in a spatter of hot oil might get a number of contaminants over their body, which in turn cause damage from the heat. Or cutting more to the point, more dangerous substances might be used - like something flammable or imported venom from other civs - that causes paralysis, rotting flesh, or so on, providing the toxin works on contact. I didn't actually mention anything about cooking (since kitchens already serve that purpose fine), and vapors seem a rather roundabout way of doing things unless the toxic substance in question only causes harm when inhaled/ingested.
So, a better example of the intended outcome might be "The boiling plump helmet oil splashes onto the goblin, covering his upper left arm in boiling plump helmet oil!"
Could conceivable be performed with an attack type similar to how catapults/ballista work, except vertical rather than horizontal, and with an effect of something like deadly spittle, spreading contaminants in an area but otherwise causing relatively little harm.