Yes, eunuchs were often created in order to be sex slaves, and remained sexual (as transgender women are today post-castration, as neutered dogs often are, etc.). Even Game of Thrones has a subplot about it.

I get into it more in my sacred androgyny article. The paper by J. David Hester, “Eunuchs and the Postgender Jesus: Matthew 19.12 and Transgressive Sexualities,” notes that eunuchs were “widely perceived as neither chaste nor celibate, but highly sexual and sexed beings.”