They can still get married no matter who throws the party. But the guests get the thing saying they were disappointed that the Sim throwing the party didn't get married. Well, maybe not. Seems like I do remember that the "Get Married" wasn't an option if someone else threw the party. I'm not sure on that.
If they exchanged rings and everything, I don't know why the marriage didn't take. It should have brought up the screen where you move the groom into the house. Sounds like some kind of glitch, hopefully just with that one wedding.