As others have said, it depends on what you mean by "safe".

I've been asked for things like this with my domains before, and usually I've declined. Not for safety reasons, but for coherency reasons. If the redirect is to a site that is both on-topic for my site and the other site is noncommercial and/or by someone I already have a relationship with, I'm more likely to agree to it.

If it's a purely transactional thing where my only interest in doing it would be for some sort of reward (in money, attention, whatever), then I'm not likely to agree because I think it dilutes the value of my domain.