Whales - actually, I'd give the zombies a morale of 500 or something, because there's fun to be had with it later - if you give no way for it to (currently) be lowered, you won't have to put in special instructions for it.
But I remember we talked about different behaviours before - the monsters 0 morale "run away" action doesn't need to be "flee" - it could just be "keep distance".
Some, smarter zombies, can thus make use of the mechanic. Every turn you spend close to a spitter zombie, for example, decreases their morale, as well as damage - if you do enough, they'll try to move further away until their morale is high enough again that their aggression overcomes it. If their basic morale starts at, say, 100, then they will immediately flip to "flee" whenever you are in range of them, and then return to "attack" as soon as you move out of range.
If you include the "roamer" or "shrieker" types we described before, they can have a morale modifier based on player distance and whether or not the player is awake - meaning they'll hang around the periphery unless you do go to sleep (making it fall low enough so that their aggression overcomes their fear), or attack them (raising their aggression) or otherwise goad them into attacking despite their low morale.
Not sure if I'm being completely clear about what I mean here, but the coolest situation is this:
Hulks cause the morale of nearby everythings, including zombies, to drop. Basically, even zombies know to get the fuck out of the way.