I think small amounts of either ammonia or alcohol would not harm a gray water system in the least. Ammonia would just be a plant nutrient, and alcohol particularly ethanol such as vodka would rapidly breakdown.
It probably also depends on the volume of water you have going through the system. If your dish water and shower water are all mixing you could use larger amounts of soap, ammonia, or alcohol to wash your dishes. We need people to pick 1 or the other and do careful determinations of the water flow and amounts they are using. Water companies and pesticide companies and other toxin producers may disagree but I thought those were good comments