My understanding is that any event pokemon "caught or evolved" during the event will get the special move. My recollection during Larvitar day was that people from Asia confirmed this, catching SD Ttars in raids during the event. But that event was only 3 hours long, this one is 58 hours long. Big difference.
Of course, we've never done one of these before, so this is all speculation. My gut feeling is that is exactly what will happen - pokemon caught as raid bonuses will have the special moves.
Further, it's possible that, for the weekend, Venusaur, Blastoise, Charizard, and others will return as raid bosses. Not certain, but possible. I think it would be a good move on Niantic's part to do so.
Stay tuned - we'll have answers to these questions just after 4 PM EST or 1 PM PST. Say that there's a Ttar raid that starts at 12:40 PM PST (event starts at 1:00 PM PST). If one did that raid before 1:00, one would get a Ttar with Bite or Iron Tail. If one did the raid after 1:00, one should get a Ttar with Smack Down. Note this is for the reward encounter for the raid, not the raid boss itself. That's how it ought to work, since the reward is caught during the event (in the latter case), even though the raid started before the event began. If there are new raid bosses, their eggs won't hatch until 2 PM, an hour after the event begins.
Again, this is what I think will happen. No guarantees (especially about the raid bosses - that would be a new thing).