Is there any rule against doing both? Genuinely don't know and never checked, I either get games here or, if a game's worth enough to donate, default to Patreon if the game is tame or Subsribestar if it's spicier. If you can do both... why not? Then if Patreon goes down you've already got the other up and don't lose potential fans from either.
Also if you want to keep the darker stuff but stay within Patreon's rules, you can always go the 'Dark' patch route. Use the art you want as long as you keep the in game text of a scene safe/consensual/PG13... but have a patch which changes the lines to what you really wanted as an option you privately post up elsewhere (and don't advertise that on Patreon). As long as what's up on Patreon doesn't violate their rules and you don't advertise you released a patch to add more elsewhere, they don't care if it's patched separately to have incest/rape/bestiality or hard monster stuff/hard bondage/whatever. I've said before, Patreon's rules are a twisted love child of SJW's and the Moral Majority. Just think of working around them as doing your part for freedom itself. Be a porn patriot!