Consul combined with consul-template for dynamic config changes in your environment is an extremely powerful solution which just works with minimum fuss.
Works well when deploying clusters such as zookeeper, allows all the nodes to discover each other automatically and work out their id number.
There's lots of software you might operate that requires zookeeper: kafka, solrcloud, the hadoop ecosystem, etc.
Meanwhile, consul has lots of functionality built in that makes it a snap to use for service discovery within your existing infrastructure. You would have to build all this yourself on top of zookeeper, which just provides a distributed, consistent key-value store.
So it's easy to see why you could end up with both.
Works well when deploying clusters such as zookeeper, allows all the nodes to discover each other automatically and work out their id number.