Why would Patreon care what an artist is posting on another site? They're not posting the content on Patreon so they're not breaking any rules. There's no rule that states that a creator should have a 1:1 mirror of his Patreon if he is also on another paywall site.
A creator I follow, lesdias has a normal Patreon and his Subscribestar has the more naughty stuff.
These fuckers have rule for it.
If you are a creator earning money on Patreon, we may be exposed to risk based on what you do with those funds. As a result, we may also look at what you do outside of Patreon. if you find a new and creative way to hurt Patreon or our community, we may take action to prevent it.
Of course main problem are paypal, VISA, Mastercard etc. who set rules on fiction content and they don't care about difference between fiction and reality. It's sad think about it you can earn money if you create brutal gore FPS shooter with killing innocent people, but make porn is heresy. Double heresy if you do non vanilla stuff.