Galaxy doesn't require Zookeeper (it's an optional dependency). And Galaxy isn't there just to support Quasar/Pulsar. It's there to support a distributed, concurrent, consistent in-memory database. Actors are just part of the story.

To simplify, Quasar/Pulsar + Galaxy is, in Erlang parlance, like Erlang + Mnesia or Erlang + Riak (only with a consistent database that assists in parallelization)