In my experience, it's surprisingly helpful to have knowledge of Java libraries and an understanding of Java classes, objects, etc... when working in the JVM with Clojure. Otherwise, one would need to spend time understanding streams and readers and writers and the typical mutable java collections, etc... It's also helpful to be able to find a free Java library and to know how to interoperate w/ it and wrap it up behind a nicer functional interface (knowing the connection from Clojure to the host VM).
In terms of 'useful for employers', I don't think there's anything more useful than having written and deployed Clojure programs that solve real problems. I'd say write a Clojure program, see if it's fun for you, and then go from there.