Yes, it is a older thread, but just in case some newer people see it..
The only times alignment will come into play in terms of units is if you manage to charm a creature/unit that is dedicated to the alignment opposite of you. The other time is if you are good and capture a Archon dwelling or evil and capture a Fey dwelling. You can produce units there, etc but they will all suffer poor moral because they don’t agree with your alignment.
Note that some units that are guards will have the “inherently evil” tag, but if you were to summon them/create them, they will be untagged in terms of supporting one faction or another. (Hell hound is an example of this I believe).
It seems to be a bit tougher to become evil in the game because of the undead. All undead give credit to the “good” side when you kill them. Unfortunately, even if you are evil, the undead don’t care and will attack you regardless, so you don’t really have a choice. Same for cleaning out crypts. You have to kill undead to clean them out. Now what is interesting is destroying a Archon dwelling is considered an evil act and will hit your good faction. An interesting state of affairs to say the least.