I don't believe mobs (or players) can actually spread fire if they catch alight. I know recently I was leading some zombies which were on fire around and under some trees and nada, couldn't make it spread.
Interesting timing for your post though, there was an accident the other night with someone's new fireplace resulting in the temporary loss of several nearby properties. A quick server roll back fixed everything though (luckily an Admin was on).
For those new to the game, if building fire near something flammable, remember that you need a 3 brick radius in all directions of non-flammable blocks to avoid the fire jumping and spreading.
Although the scythe isn't pre-eminent among the weapons of war, anyone who has been on the wrong end of, say, a peasants' revolt will know that in skilled hands it is fearsome. -- (Terry Pratchett, Mort)
Playing: Killing Floor - Other Stuff