I'm not sure about eucalyptus leaves, but I think I once read something about orange tree leaves- something about the oils in the leaves? I have 2 orange trees in my yard and every once in a while I stuff some green leaves on top in the smoker, if anything it at least cools the smoke down and keeps the smoker from shooting flames when it gets too hot. Keep us updated if you try it, I've got lots of eucs around here too...