[Sethomas]

Hmm, Acts 8 was apparently what I was thinking of, but it just talks about an Ethiopian legate of the Queen being baptized despite being a eunuch. Eh.

As for later Christianity, castration was pretty taboo except as a secular punishment (I have a really fun story somewhere about a 14th Century lynch mob hanging people upside-down by their scrota) until around the Baroque era when castrati became prized singers. However, as far as I know they were still allowed to participate in the sacraments, they just were forbidden to marry because of their inability to consummate.