It is not. It exists, yes, but at most clubs even soliciting swinging could cause you to be banned.
Yes, swingers are more relaxed about nudity to begin with, so of course they would be at naturist gatherings.
There are swingers in church groups too. But swingers have their own venues and their own clubs.
My wife and I summered at nudist resorts for over 25 years. Yes, we knew some swingers and some of the more careless ones did get booted. There were others who probably were, but they didn't solicit or discuss it.
We felt the clubs were overly strict about this, but they wanted to keep a more "wholesome" image. I think most of us felt live and let live was appropriate unless someone just wouldn't take no for an answer. Then we'd threaten to dime them out.
A sad story about a nudist couple who were very active swingers. We liked them both, they were fun people. She died from sexually contracted hepatitis and he committed suicide shortly after, blaming himself for her death.
Sad..