While maybe not strictly necessary per se, it's a great way to get a foot in the door, and provides a great way to foster advanced type systems and functional programming (I personally find it to be a really fun language to write in to boot).
What job can this do that can't be done via sql. dealing with unstructured data?
Isn't that just a result of everyone being into Spark a few years ago?
SQL is also an amazing tool and you should definitely learn if but there are a lot of DE jobs out there with Scala in the "Requirements" section of the job listing. Parts of the industry might be moving away from it, but if you're looking to make a jump into DE I think you're hamstringing yourself by avoiding Scala.
I would learn python. Its the number one language outside sql.
edit: Guess this was pretty much in the post.