The harrier's nozzles would always have a net forward angle at the hover (still air) to offset the intake momentum. Essentially the engine sucks in a large massflow of air, so it effectively "sucks itself forwards".
PDR. Surely Intake Momentum Drag is the result of the air coming through the intake (not sure it's sucked-in but I know what you mean) and then being 'stopped' at the engine. The engine is producing thrust vertically so the net momentum is rearward, i.e. it would push the Harrier backwards? You therefore need a tad of rearward nozzle to countwract this and remain stationary.
With the intakes forward of the CofG it is this Intake Momentum Drag that makes the Harrier directionally unstable in the hover and caused all sorts of nasty problems if any appreciable yaw is allowed to develop. Hence the yaw vane on the nose and I believe vibrating rudder pedals!