Patreon is relatively safe in that regard: They don't have much focus on discovery, no ad-placement to worry about, ... People interact with it primarily through deep links to invididual creators pages, so the "neighborhood" is less relevant. They've always been far from being a "porn site".
The answer to all 3 responses is 'perception' less so 'what happens on the site' although they are related.
Amazon is not known for porn. I didn't even know you could get porn there. Certainly, it's not 'online porn' which I would imagine would be the primary issue.
Tumblr became a place known for adult content so it was a problem. If Amazon started to do a lot of digital porn, like PornHub, it would be a problem.
If there is no 'search' on Patreon ... maybe they could keep it hidden. But it's a big risk.
There's plenty of adult stuff sold on Amazon yet I still would like to sell my new line of e-books there.
I mean, if Patreon provided a good service and the porn was hidden away under the default filter and not visible from my subsite or the homepage, I don't see at all why I wouldn't launch a product on it if I decided the business model was a good fit.
Would you launch your new line of e-books on a site that is 95% porn and well known for porn?
No.
If you're a porn site, then you're pretty much going to be just that, it's its own content vertical, fairly distinguished from everything else.