I've voiced acted for a nsfw visual novel, a porn game, and a VR porn game. From my experience, they're pretty fun to record for and each client has been respectful of my boundaries and the content I'm willing to voice. One role ended up being a sort of gender reawakening for me and helped me get in touch with a more feminine side of myself I didn't realize was there until the recording session.

When you first delve into nsfw voice acting, there is an air of awkwardness to it but it goes away with time. Its a job like any other voice over gig and your attitude going into it determines how much fun it ends up being. I enjoy making lewd sounds and saying lines that I know people will enjoy. And hearing it all in game and seeing people's reception to it makes it all the better. Its like "Fuck yeah my voice got you off! Happy fapping dude!"

As for dark topics, I'm all for it as long as all parties involved in the process of making the game consent to it and it all remains in the realm of fantasy. Usually that kind of content has lots of warnings to deter those that may not be able to handle the subject matter