Okay, so in this situation there's really nothing to discuss -- the bride and groom were not only fine with it, they were in on it, so there you are.
But in general, I agree with Celleach: fine to propose at a wedding, but not publicly. Whether you tell anyone or not until after depends on a lot. I would run that by the bride and groom.
I am not crazy about public proposals anyway. Too awkward if the answer is anything but !!!!!!YES!!!!!!! right off the bat, and to me they seem like a little concerned with "look at me!" (and even "aren't I clever!" when it is something gimmicky) for something that is so intensely personal.
At my daughter's wedding last year, a cousin told the family she was expecting. She and her DH didn't make an announcement, word just got around during the cocktail hour. She hadn't said a word at any of the socializing the 2 days before the wedding; she said she was even wondering whether it was okay to mention it at all, so I'm guessing she was waiting until after the ceremony. But I am so glad she didn't wait! Our family is so spread out, it was wonderful to be all together to get this great news -- her brother and parents and grandparents, all of whom live far from her, were all there. I'm sure it didn't bother the HC a bit, either, and it didn't draw the slightest focus. I really loved it; it was like a lovely little segue from one important transition (and happy occasion) in the life of our family to the next. It wasn't until afterward that I remembered that the pregnant cousin was 2 months old when I got married, and my wedding weekend (she was with a sitter during the wedding itself) was the first time we all "met" her. Nice little circle-of-life symmetry.