I loosely swaddled my second child from time to time when she was about 5-7 months. I swaddled her in cotton and she wore a prefold belt and something absorbent. I just pulled the blanket aside from her lower body too pee her.
This time around DS wears a homemade fleece cover over a tiny flat and if he needs to be swaddled, I wrap up his arms only. He kicks when he needs to pee, so if he was totally swaddled I would have a harder time knowing. So far (10 days) he sleeps pretty well without swaddling. I pull his cover down to pee him.