I'm still on Step Five of the Snowflake outlines. I'm currently writing the antagonist's outline and should be ready to start Step Six by sometime tomorrow. Since I have another long weekend off work this weekend I can hopefully get a good chunk of it done this weekend.
But writing a one page outline of the storyline from the antagonist's perspective is an interesting exercise. It forces you to think about why they are opposing the protagonist. People don't - in general - do things for no reason. Outlining for the antagonist can make any holes in their motives become obvious to you. This antagonist has a far more interesting motive for his actions than in my original idea now. In fact from a certain perspective he's not even wrong - it's what he does as a result of his conclusions that's the problem. It's proving fun as well.
I think that if you are worrying about the possibility that your antagonist might be two-dimensional doing an outline from their perspective which makes their case would be an excellent exercise.
If you do try it don't forget to comment and tell me.