Using the herd feature you could generate mini monster camps by making the herd spawns be things like fire pit, tent, monsters, treasure. With the right mix of random probability you can have little mini monster camps spring up all over your world with random chance of treasure or unique items. If you make your static objects have nav mesh obstacles then they will be properly navigable after spawning on existing baked navmesh. I haven't tried this yet, but seems possible.
You could also spawn an entire prebuilt camp as well, but getting the elements to fit to the terrain could be challenging unless you have a custom script on them to snap them to the terrain when they spawn.