Oh goodness, I know a lot about backyard pond bogs but nothing about “natural bogs.” In general, yes, a bog will help with water quality, but the kind of bogs we have are self-contained and plumbed as part of a lined pond. Any time you add plants, it’s a good thing.
I’ll let someone else chime in on this one. Also, this is an old post, so I’m going to see if the moderators can start you off in a new topic. Your chances of being seen by more people tends to get lost in these older posts.