Hi Zerdath. This is the official line:
Games containing mature themes or material that is not suitable for young audiences should be very clearly marked.
This means, yes, you can create NSFW games but bear in mind that there is no minimum age for the jam. Please keep the game page, title and cover image clean. A very obvious warning about graphic violence, extreme images, sexual content or similar should be included in the jam submission (first comment maybe) and game page.
If you have any doubts, feel free to reach out.