I recently came across this question on-line and whilst I was looking at it and it made me think of both my past and my possible future as my answer to this question the honourest answer is
Yes in fact to my knowledge it has actually happened to me at least twice in my life-time, once in 1983/1984 at a relatives wedding when I was still in diapers as a toddler/child although I can barely remember that occasion although I was probably in a Pampers or Huggies one on that occasion.
And the second time in 2013, when I wore a diaper to my cousin's wedding in Leeds on that occasion I wasn't obliged to wear one but I thought I would any-way as I am partially incontinent see my previous replies for more information.
I wore a pair of boots stay-dry slip in large size, and I really enjoyed it as they kept me dry and cosy for the 5–6 hours it took including the reception and after wedding dinner.
And as it was raining on the day I had my rucksack with me with my raincoat and nessiasry changing supplies which were hidden in the bottom of my bag.
And thankfully I was able to change myself into a fresh diaper/nappy or two during the whole event in the toilets provided at the venue,
as I would not have liked to give the game away by having a smelly butt or stale urine Smell as specially as that would have been very embarrassing.
Thankfully I wasn't the only one wearing them as there where other relatives that had toddlers/children in them and some of the older relatives that where elderly also wore them so nobody batted an eye lid to me wearing one on the day.
As for if anyone else no body noticed me and thankfully they did not say anything about it,
so that was okay because thankfully I didn't have to answer any awkward questions which would have been highly embarrassing as specially in public.
And as for the wedding the whole day was magical in the scene of the fact that everything went to plan not only for my cousin on the day he married his then new wife.
But also for me, as I had planned in my head what to do, but no pun intended had no experience of until it happened,
Would a wear a diaper again at a future wedding or christning well the awnser is yes
Although speaking of which the first time I wore a diaper at a christning was of cause my own in 1980, not that I can remember that day as it was so long ago.
Although that's a subject for another day. however If andwhen I ever am invited to go to a future wedding I would wear a diaper again only this time something more absorbent,
As 2013 was the first time since I was a child that I wore a diaper/nappy to such a occasion.
Hopefully this will answer your question.