When the first bloom reached male anthesis, I did not see any pollen when i checked after sunrise. That previous night, however, we had a brief shower and I had hopes that the problem was that the rain washed the pollen away rather than that my hybrid was sterile. A second bloom has opened and matured, though, and this time I saw (and used) abundant pollen. So Imperial Dark does produce pollen, as does Imperial Giant. Now it is a waiting game to see if I get seed set on crosses using this pollen.