Redis began as a caching database, but it has since evolved into a primary database. Many applications built today use Redis as a primary database.

https://redis.com/blog/redis-cache-vs-redis-primary-database...

Very much seems like an acceptable use now

Redis can't have a working set larger than memory. It has no mechanism to page data to disk. If your data set grows too large, you're hosed unless you add more hardware.