ZeroMQ sockets can connect or bind, and this is independent of the socket type. If you want to load balance requests against a dynamic number of responders, just have the responders connect their REP sockets to a set of bound REQ sockets.
ZeroMQ merely solves exposure of sockets as queues. In all distributed systems, there must be a set of known hosts, or discovery becomes tedious. DNS is an easy way to solve this.
ZeroMQ is an abstraction that hides a lot of complexity for you in the name of convenience, and there's no reason why it couldn't abstract discovery, too. Instead you have to build it from scratch for every client app.
