Prior to the testing with Soris, I invaded and hosted for a while in the Township with the ring on. I won every fight except for one, including a gank, so I had some quality test material time. I incorporated kicks, backstabs, ripostes, R1 spam, and anything else I could think of to pass on the effect. I am now suspicious that anyone who owns the DLC might be immune to this like said before. (Soris and I tested in both the Township and Catacombs so it's not just the DLC area. ) We also tested with the ring not in one's possession.
P.S. - If you really want to improve your PvP game, put on the Calamity Ring. Not only do you take double damage but you will also be sacrificing poise or defense if your original ring was Wolf or Havel's. It's the ultimate ring for making yourself more careful; I was actually landing more ripostes than normal as well.