Well, I guess that depends on what kind of zombie you're talking about. Zombies created by viral contagion might be susceptible (though said virus might attack any other biological agents that attempt entry, after all, what's the use in engineering a virus that would be so easily defeated). Or created by the 'Zombie cocktail' featuring Carribean Blowfish poison. Chemical agents might work on them, since they are alive. Actual (mystically/magically risen) undead zombies might not be sisceptible because: 1) they're already dead, so there's not brain or nervous system activity to disrupt; and 2) as true undead entities, they are probably in a constant state of decelerated decomposition, which means that they are constantly teeming with all sorts of nast bacteria and viruses that would kill the living. The second deadliest bite in the world, after that of the Komodo Dragon, is the bite of a living human being. The human mouth conntains 23 kinds of bacteria, which is about 18 more than dogs. Imagine how much and what kind of bacteria is in just the mouth of a rotting, animated corpse. Not to mention the kinds of bacteria to be found in said animated corpses stomach, liver, kidneys, intestines...
And as for chemical agents, seeing as how they have mystical/magical energies coursing through their bodies, and none of the conventional bio-electric impulses, I don't think chemical agents would have anything (brain function, nervous systems, etc.) available to disrupt.