My team has been using Clojure for close to a decade, and we found the opposite to be the case. While the pool of applicants is smaller, so is the noise ratio. Clojure being niche means that you get people who are willing to look outside the mainstream, and are typically genuinely interested in programming.

We also rarely hire devs who already know Clojure, and we typically just train on the job. It's really not hard to do when you already have people who know the language on the team. In fact, if somebody can't learn Clojure, I would question if they can learn to work on a large project in general. Dev practices, architecture, code styles, tooling, and so on tends to change quite a bit from company to company. The language is only small part of that.

In case of Storm, Apache commons is run by Java devs who have zero interest in learning Clojure. So, it's not surprising they would rewrite Storm in their preferred language.