For vector tiles osm.org this is not the case. They should be generated on the fly from the database to show mappers the current state of the map with minimal delay. Yes, the resulting results can be cached like static files, but much more work is done on the server.

You can learn more about this in the blog of the developer who develops this tile server: https://www.openstreetmap.org/user/pnorman/diary/403600

p.s. current link to the demo page: https://pnorman.github.io/tilekiln-shortbread-demo

OP asked "Does this reduce the operating costs of hosting OSM-based maps".

openstreetmap.org has a very complex setup for real-time updates, but in general, hosting OSM-based maps is much cheaper with vector tiles.