Here is what I know about Celebrity. We have taken two Celebrity cruises. On the first, they did not have a chaplain aboard. On the second, a Catholic priest was the ship's chaplain. Since we are Catholics, we went to daily mass (well....most of the time) and went to the group "Renewal of Vows". It was a very low-key ceremony and only attended by four or five couples but, it seriously conveyed the meaning of marriage and the recommittment of those vows. In short, it was a great ceremony. We did get a certificate that we did renew our vows.
On Celebrity, I really think it depends on whether or not there is a chaplain aboard. On our second cruise, we had one. On the first, there wasn't a chaplain.
I suspect it is kind of hit or miss; at least on Celebrity.
Shirley and Les