You are right about the positive and negative effects and the presence of certain units.
However, if there are demons, undead and humans in an AI army, the humans have -2 morale, but in the end, it is not calculated and all their stats are as they should be. That is what I meant. I guess it needs clarification.
BTW, when you guys see I'm not done writing, please don't rush into conclusions... I got used to saving my work from time to time in order to preserve it from random PC blocks, power outages and such
EDIT: Fixed and clarified.