When I throw a game there are a few types of Zombie and not all of them are equal.
First we have the standard issue zombie in the tradition of all the zombie movies of the 1960's. These zombies are mindless shambling corpses with little will and no concept of tactics. They rely on the herd of zombies approach and overwhelm an area or heroes. These zombies attack the closest living human and try and eat them. Unfortunately there are just not enough zombies in any of the official dungeons to utilize this tactic as an EWP.
Second is the classic style Dungeons and Dragons zombie which is similar to the above zombie in that it is mindless. It relies on the overwhelming herd of zombies just like the above zombie. This zombie is different only in why it is a zombie. Instead of a virus causing the condition of being a zombie this zombie is a corpse that is fueled by 'Negative material Plane Energy'. Once you are slain by this zombie you become a zombie and join the herd. There is no real difference in the final outcome of this type of zombie and the first one spoken of. It is just a cosmetic difference.
I have issues with type 1 and 2 Zombies wielding weapons of any form. Unfortunately most miniatures depict them with weapons.
Third is the semi intelligent zombie. Maybe it is a more evolved form of type 1 or 2 zombie but it is much more dangerous than them. With a limited amount of intellect left it loathes and despises life, seeking to transform the living into zombies. This zombie should be allowed to wield weapons and employ basic tactics. To represent the improvement I suggest adding a dice for attack and defense and play smart with this dude.
Fourth is the fully intelegent zombie. This dude remembers all from its past life and is highly dangerous. If a spell caster or warrior hero in past life one can expect to face an opponent with the ability to cast spells or in the case of the warrior wield powerful magic items. These zombies can mentally control other zombies of lessor stature. This zombie is never a victim of a zombie virus, but rather the victim of foul magic's that transform them into the living dead. For Hero Quest purposes I would give this zombie 2 extra dice in attack and defend an extra point of Body or two, plus they should be equipped with spells or magic weapons.
Type 5 zombies are the Zombie Lords. These are magic users who have embraced dark magic's, transforming themselves into the living dead. They maintain complete control of their facilities. These dudes create and control type 2-4 zombies. They are end boss type dudes and they are the most dangerous of the zombie types. Typically one can expect such monsters to be fully cognizant and capable, utilizing tactics, logistics and magic to acquire power. These guys would be as the Witch Lord in power levels and he would suffice very well for a campaign.
Type 6 Zombies are totally different. They are zombies that are victims of a fungus. These zombies have none of their own intelligence left after the transformation but the fungus that makes them zombies does have a rudimentary form of predatory intelligence. These zombies are cunning and calculating, but they are not capable of wielding weapons, instead relying on hand attacks and spore cloud attacks.
Once exposed to a fungus zombie if it touches you, you get any part of it on you, or if you are caught in a spore cloud, then you will become a zombie in a few days. The first day the victim will feel ill, but there will be no major problems. During this time there is chance to heal the infection. Two healing potions followed by a healing spell is the typical counter measure. The infection is rather insidious. For HQ I would use this zombie in a tactics minded fashion but no adjustment to the stats for basic zombies. For their spore attack I would roll three attack dice and the Hero rolls defense dice. If the hero does not defend against all points rolled by the zombie then the hero is infected.
Type 7 zombies are not really zombies but they act the same as others. These are the mindless minions of the diabolical forces. When a demonic entity takes over an area it will enslave those with lessor minds and will.
These zombies follow the will of the entity controlling them. They are harmed by holy water. Other than being harmed by holy water they pretty much conform to the statistics of basic zombies so no adjustments to attack, defend or body is needed. These zombies do not turn people into new zombies, however the diabolical entity may decide to animate these corpses and make them real zombies. For HQ I would say that a vial of holy water rolls 2 attack dice and if the zombie fails to defend against a skull then the zombie is destroyed.
The real problem I find with zombies and HQ is that there is not a large enough area and there are never enough zombies in a dungeon to make true effective use of them as minions of the EWP.