The US has also recently found men doing this sort of crime:

https://en.wikipedia.org/wiki/2024_Cornell_University_rape_allegations?wprov=sfla1

But I am not comfortable calling it a fetish when it's being carried out IRL (it's a crime). I also am not sure "sleep fetish" is the motivational cause. I think these men are just rapists.

My understanding is that rape is often opportunistic, the rapist does so because they want sex and are willing to use someone elses body to get it (rather than being driven by some ideal of "sleep sex").

If it involved giving a "forget drug" doesed beforehand they'd happily still do that rape. If it involved someone being bound in an unwilling bondage scenario in the dark, and them taking turns - they'd still rape.

They're rapists. I think that's the motivating factor. They're not motivated by a fetish that we can shift "the influence" to, they're just rapists. They'd make the decision to rape in lots of different scenarios.