I remember reading a post a while back about this and that it is definitely not ok to use in the great outdoors and that it is actually worse for the water supply than synthetic detergents are. I am only restating what I have read here and personally have no knowledge of this.
My house is not attached to the town septic system, instead I have installed a BioCycle septic system. Everything that goes down drains in my house goes into my BioCycle where it works its way round some chambers where natural bacteria work their magick on it. When a certain amount of liquid is in my BioCycle the excess liquid comes out onto my vegie garden.
Due to recycling all liquids used in my house I have a list of products that are suitable. I contacted the people who check my BioCycles ph every three months and asked them about the soap I make. They rang me back to say it's all safe. Plus due to there being a limited amount of soap entering my systems on any day ... any risk is further reduced.
I have a special interest in this since I recycle my gray water for my garden. Out of all the soaps I've seen on the market, it seems a homemade one, from natural oils that would biodegrade well on their own, would be safest. There are no petrollates and no carcinogens like manufactured "soaps" have. I found this interesting piece on the chemicals found in a lot of our beauty products. http://blogs.dickinson.edu/ecofeminism/tag/softsoap/
Oils that biodegrade anyway, plus an alkaline product that is close to what we find in nature, chemically changed to a salt. I think it's better than most things you could buy. I'm not going to recycle the water for my dogs, but I feel it's fine to use in moderation around the plants.