I don't think they can, my last match in the city map I must have walked over a dozen or so of our team's corpses as a terminator and got no weapons.
I don't think they will have it, storm bolter is strong enough. Assault cannon is probably reserved for the upcoming dreadnought.
You can pick up weapons of sub-classes that belong to your own class when you run over an dead mate. Eg. if you are tactical you can pick up the chainsword and extra nades(?) off the dead.
Some kind of Terminator that would be best suited in an offensive role... An Assault role if you will.