Basically, Patreon doesn't pro-actively do anything about "adult stuff." They only act when they get a complaint. There's actually a reason for that - if they try to curate all the content on their site, they become somewhat responsible for things they miss. If they sit back and only react to complaints, they're (somewhat) protected under certain aspects of US law.
So, basically, if someone shows up and says "I own the copyright to that clip - they don't have permission to use it," they'd react. But it'd probably have to be someone with "standing" - somebody showing up and saying "they're using someone else's stuff" is probably insufficient, as they'd need/want a complaint from the actual copyright owner.
