While not 100% guaranteed fact, it would appear the slap was real. According to those who attended and those at the table with Will and Jada. Seems as if Will originally thought it was funny, till his wife asked him if he was going to do something about it. Geez, hasn't this woman already emasculated him enough in public already. Hate to say it, but she seems to have total control over him. She has messed with his mind so much; he doesn't know how he should act (as their past public appearance admissions would indicate).
While I can somewhat feel a little sympathy for him, it's still no excuse. He needs to get a grip and take back control over his personal life issues, instead of lashing out at others for his stored-up anger.
Can you imagine if Ricky Gervais had hosted, what things he might have said? Jada may have expected Will to take even more drastic measures.
Simply put, when you attend these kinds of events, you know and expect the host comedian to be roasting people.
If your ego is too fragile, you have issues with self-control and may be having personal issues in your life, it's probably best you do not attend such events.