Right so, when you open the app, you must choose a server to connect to, for the purposes of app verification, you provide a server with heavy moderation.
I could see apple having issue with providing pre-filled server selection, but if you had to manually enter a domain, I would be interested in how they would move the goal posts to deny an app like that.
I think a good example here is Telegram. Telegram did not used to surface NSFW chats on iOS to comply with the App Store. But you could still join the channels manually. However, on a whim Apple decided that wasn't enough and now you cannot access those at all on iOS, you get a message saying it's blocked.
Of course, it wouldn't be able if they were committed to equal treatment, so the counterexample here are the many Reddit apps on iOS. You can join NSFW subreddits and they are allowed so long as they aren't shown by default. The only explanation is here Reddit is used by Apple employees or they know there would be an outcry if the rules were evenly applied.
Their goal so far has been avoiding casual exposure to anything less than family-friendly. If a user has to go out of their way to procure offensive content it seems Apple is not that concerned - browsers, mail clients, IRC clients, etc is fine.
I could see apple having issue with providing pre-filled server selection, but if you had to manually enter a domain, I would be interested in how they would move the goal posts to deny an app like that.