Fan patches that "restore" that content can cause trouble if the patch is in anyway connected to the developer.
Yeah, if it is referenced or even mentioned on Patreon, the developer will have big problems.
There are devs who have never had a problem with any of that so it seems like a crap shoot. I never really know what sets them off exactly.
Some developers have flown under the radar with their incest games, if they don't advertise them as such - even without any patching. But sooner or later somebody complains to Patreon, and the developer has to scramble to modify the game (however they decide to do that). Then again, some games don't actually implement full incest content for a while. But when they do, they are in full jeopardy.
But, there are scores of incest games on this site that coexist just fine with Patreon. They use patches, or relationships defined within the code, or whatever. These Patreon minders don't ever play the games. They don't have the time. If you've ever tried to contact them, they hardly have time for a simple (non-automated) response. [I don't know what they spend their time on, but it's not Subscriber interface.] So Patreon relies on what gets posted on Patreon. If someone tries to snitch on a game that uses a patch, the developer says that he/she has no control about people who patch or mod their games, which are in the public domain after all. [A poster pays for access to the game, and can do whatever the hell he/she wants with it.] For developers who define relationships in the code, having the default being a non-familial relationship seems to work there.
I just clicked on the 'Incest' tag at the top of this page, and got nearly 1000 [49 pages @ 20 titles/page] results! So, the incest fetish doesn't appear to be in danger of going the way of the great auk any time soon.