I think it's a little ott to be honest.
On the night time do we've got one of my h2b's ex's attending, with her partner. However, i understand that h2b as moved on, she is from his past (and in my opinion a bit of a slapper anyway lol) but it's not going to ruin my day. just because she'll be there for a time, does not mean that i have to sit all night and socialise with her.
Your oh has clearly moved on, and i wouldn't let the attendance of an ex put a downer on your day. Your oh is there to marry you, and thats what you need to not lose sight of :) xx