Indeed, Swancon Natcons always award the Tin Ducks as well, and often other awards (such as the Chandler, or the McNamara award) are presented at the same ceremony.

But seriously, I think adding categories to the Ditmars (if you think there is a need for them) is a much better idea than starting an additional set of awards. Running a set of awards is a major pain in the arse (believe me, if I didn't already know, I would have learnt that one in the last few weeks) and the number of categories is a relatively small factor in that.