Okay, I did a down and dirty search for the ingredients and here are two from the ones I came up with. Warning! The first link has some strong language, the second gives us the basic info on just what the icthammol is. Would it work on a human? Sure, I believe it works by causing more inflamation and making the body expel the poisons quicker. With a duck? I'm not so sure about that....remember, the pus in poultry isn't watery like in humans, it's a harder cheesy like thing. If you had Iodex as the drawing ointment then I'd say yes it would work, after a while. If this were my bird and it had heat in the leg as you say, I would be giving it an antibiotic as soon as possible, then I would go to work on the swelling with very warm soaks with iodine or betadine in the water and then the topical application of undiluted iodine after, over the whole area of swelling.
I just got through reading something about a case of bumblefoot that turned septic, in this case a chicken. That person too tried using topical ointments, triple antibiotic cream, with no internal help of an antibiotic. Unfortunately, it was too late for that and the bird died. I didn't save the link, I'm sorry. If you do a search for bumblefoot and sepsis, you might be able to find that particular one as well as a host of others.
http://morsdei.wordpress.com/2009/08/21/not-so-safe-homeopathic-ingredients/
http://www.ichthyol.com/ichthammol_1.html