I've not observed any nectaries or other bits that the ants feed on specifically on my Catasetums. But you are right that the inflorescences attract ants. Catasetum maculatum is entering the blooming season now and several of them that have a constant presence of mean little ants on the buds. My guess is that they are exuding honeydew. It's something I've observed on quite a few orchids such as Encyclias and Cohniella.