I have a hard time believing that modern search engines are so incapable that they have to devalue redirects to the point that honest users have to worry about it.
Well that's just what I know about the things we did then. I'm not working in porn anymore, so I'm missing the new cool tricks, or abuses, depending of your point of view. But the community is VERY creative.
Now the last time I did change massively URLs for a client website and noticed a significant drop in traffic that took a few months to recover was years ago. So the situation might have changed. But I'm not going to test that assumption with my clients money :)
It's been a long time since I accidentally got to porn on the internet. I think that kind of thing is mostly dead (although some of the 'related articles' sections look pretty iffy), and instead porn monetization has moved towards people intentionally looking for porn.
Now the last time I did change massively URLs for a client website and noticed a significant drop in traffic that took a few months to recover was years ago. So the situation might have changed. But I'm not going to test that assumption with my clients money :)