There are many companies using Clojure large and small, nobody actually using the language has problems hiring people for it. This is not a theoretical debate, there's no evidence to support the notion that Clojure is hard to hire for.
In practice, the language is a small part of what a new hire has to learn. Each company has different processes, tools, workflows, frameworks, and so on. A language is only a small part of that.
While there are obviously companies where Clojure wouldn't be a good fit, the reasons wouldn't be that it's hard to train new people to work with it.
However I question generalizing from 'this was not an issue for my team at my company' to 'this should not be a concern for any company under any given constraints'.
I don't doubt most devs wouldn't have problems learning these concepts. It's whether business have capacity to allow those devs to onboard in such a fashion, knowing that different business are subject to different constraints.