This is very cool, and quite surprising. Cleaner fish are thought to be among the most intelligent fish because of the complexity and danger of their feeding strategy: it takes careful planning and quick thinking. But they aren't tied to any particular species of host or general tactic; naively I imagine cleaner fish are more versatile and adaptable than cone ants.
It would be interesting to learn if this occurs with other species of ants. I suppose until now nobody thought to look.
Cooperation and symbiosis are very general survival strategies. They apear at all levels of the biological abstraction hierarchy, all the way down to mitochondria, which are almost certainly descended from what was once an independent organism. In fact, even a genome itself can be seen as a collection of mutually cooperating replicators. No intelligence is required for cooperation to evolve. It's a straightforward consequence of game theory.
It would be interesting to learn if this occurs with other species of ants. I suppose until now nobody thought to look.