I tried germinating Redbud a few years ago with no success. I'm embarrassed to say that I did not keep notes and don't recall exactly what did not work for me. Dirr & Heuser suggest a three month stratification period. Do you know if that requirement has been met?
The seed coat on these is hard and, as you implied, scarification seems to be beneficial. The same text cited above also notes that a water soak as hot as 190F will help. Another possibility is a chemical soak in Sulfuric acid. A different source recommends physical abrasion with sandpaper followed by a 5-10 hour hot water soak. Let us know how it goes.