Well it is highly agreed upon that the form was developed in Shaolin by Boddhirama as an exercise for his disciples. From what I have read about it, Sanchin is almost as generic as saying karate. There were many forms of Sanchin which has stemmed from the original version taught by boddhirama. Higaonna is credited for bringing a version of it from China to Okinawa. His teacher was Ryu Ryu Ko. It seems that the only mention of Woo Lin Chin is through the Isshin-ryu lineage where Higaonna was said to learn Seuinchin kata from him, which is different than Sanchin kata. I have yet to see any other reference to him. Ryu Ryu Ko was said to study at the Shaolin Temple was not a monk at the temple.
The problem is that because there is so much myth regarding the ancient karate masters no one knows for sure who it was that devised the sanchin kata into karate in the first place. But it's premise is to develop concentration and focus to help harden the body to withstand strikes and blows. Unfortuantly a lot of karate-ka don't know how to properly utilize this technique because the proper breathing and movements have been changed from the original variation into something that just premotes a distinct set of postures that just help to focus and concentrate. The real principal of iron shirt training is to help promote health and vitality which is why the sanchin kata ( according to what I know is why it was implimented) as a way of preperation before training.