I'm not sure if I understand but do YOU actually want your ex wife to attend the graduation party in your house?
I think it would a bit different if you asked your ex wife to a party that you and your wife are holding or something similar because the children would not be involved but when it comes to your children, well, you are asking yourself: wouldn't they be a bit upset if their mother was not at the party - I think they would, rather!
As long as your ex-wife and your wife can behave in each other's presence I think it would be fantastic for your children to feel that you can actually be under one roof and celebrate something they have achieved. Maybe you should explain things to your wife and tell her that you want to invite your ex-wife because you feel that it is very important for the children. Perhaps tell her that your ex-wife will be there like any other guest and that her presence does not mean anything else to you but that she is the mother of your children.
Many people here struggle with jealousy but it does not mean that they think jealousy justifies unfair behaviour. An insecrue or jealous person can sometimes be quite selfish although he or she does not necessarily realise it at the time. I am one of those 'jealous posters' here so I feel I know a little bit about what I am talking about!
Anyways...However it goes...I think you should pay extra attention to your wife and tell her that you are so glad that you will be able to celebrate the graduation together and that one thing that makes it so special for you is that she is hosting the party with you. We all want to be generous hosts and hostesses when it is a special occasion and I am sure she is no exception.
All the best