Can a person in his first year of availus go to a Shollom Zochor?

According to the Gesher Hachaim ( chapter 21:12, 8) since the se'uda takes place on Shabbat, the avel would even be able to take place in the Brit itself after Shloshim for one's parents and after shiva for other relatives. However, Rav Moshe Feinstein zt"l makes the reservation (אגרות משה יו"ד ח"ג, קסא ) says that only a relative or a close friend is permitted to participate in the Sholom Zachor because if he didn't go his absence would be evident and would publicize his avelut on Shabbat which is forbidden. (See also Mourning in Halacha chapter 25:15)