Have you not attended many non-traditional marriages? I've been to a wiccan wedding that was officiated by the groom's brother, and a goth wedding (dress up, on Oct 31st!) officiated by a friend of the bride & groom. Generally when you step outside of the traditional church-and-clergy model the couple chooses someone they feel close to and respect. I don't see why that should set off any alarms.
Recently, LWers Will Ryan and Divia Melwani (now Will and Divia Eden) were married, with Eliezer Yudkowsky officiating.
I've been to 40+ weddings in my lifetime, and this was my favorite ceremony yet. Here is the video, and below is the transcript of Eliezer's... what's it called? "Blessing"?