I would say it all depends on the situation. If it was on bad terms, then no. If you have kids, then yes. If you don't even talk to them anymore, then no. If you still remain friends, yes.
You have to think about the situation. How will it affect them and you if they were there? Would either of you feel uncomfortable? Does one of you still have unsettled feelings? Do you have kids that will want them there?
There really isn't a straight forward answer to this. You just have to think about them and yourself. Would it benefit them or you in any way? Know the feelings between you both. Then, go from there. If you think that you might not want to be there to see them get married again. Then, maybe you should think of them. Give them the courtesy that you would expect.