I don't see how it sounds like you'd get a granuloma. It sounds like the sperm are destroyed as they pass through the vas deferens but are still washed out as they normally would be.
Ah, I did not read up apparently. I thought this was essentially gluing the vas shut with a polymer that was reversible. According to the wikipedia entry, they don't know the exact reason it works (what?!). Very interesting.. I had overlooked that.