I've had colleagues who were dedicated Emacs users, yet didn't know anything about Lisp.

This is not surprising; it's no different from Vim users who have never written or debugged a line of VimScript.

Rubbish. Speaking as someone with seventeen-odd years of professional C# experience and no professional Lisp experience, Emacs Lisp is both easier to learn than the Visual Studio SDK and, more importantly in the long run, far more likely to be worth the bother[1] for personal use cases.

[1] https://xkcd.com/1205/