Ravener
Raveners, in a way, behave like Assault Squads. They really focus on being in close quarters, they both can ignore difficult terrain (Though that's because Raveners can dig tunnels through the terrain as opposed to jumping), and both are ill-suited for dealing with lots of dakka. Fleet also helps them to harass some unsuspecting targets, but not for any long fights with, say, any MEQ. However, don't count this as being incapable of ranged battle at all. Provided one has enough points, the brood's members can be upgraded spinefists, which give it a good weapon, if not pretty low, a devourer which can chop flimsy guardsmen and trap them there, and the deathspitter, which is largely better than the devourer. Also, they can switch a pair talons for rending claws, which can help cut through the numbers.
In Dawn of War II, one of the heroes for the nids, the Ravener Alpha (Essentially just a bigger Ravener), learns to take a page from the Trygon's book and build large tunnels for allied units to crawl through.