I attended a wedding last Sunday, which was Yom Yerushalayim. The chattan and Kallah did not fast as they claimed that since it was a day when they did not say Tachanun, and they said Halel, it was considered similar to Rosh Hodesh or other holiday that would exempt them from fasting.
I didn't have time to ask the chatan of the source for this ruling. Is someone aware of anyone that rules this way?