Thanks for posting as my boy Blaze has the Hard Swollen Sheath also, so I have been following your post. I had come to the conclusion that his is from hormonally active tissue in the groin area (he is MS/IR/PPID) but your post have me really confused now. May I ask the reference to the “hard” part… when feeling that is it like irregular lumps of hard tissue? Blaze feels like there is something inside that is hard and rough, sharp even….My vet has never seen or felt anything like it. 

Did your guy have blood work that showed infection? How was it determined, as I might need to get Blaze more blood work done.