I'm not 100% sure yet since this is the first event after launch but the event girls in the beta event were added to the gacha so I would assume these girls get added as well. Maybe not Naku if they follow seasonal limited girl patterns from other games since she's Christmas themed but the other 2 aren't Christmas themed. But this is just speculation.

On another note, the fandom wiki has several upcoming girls already listed. Does anyone by any chance know where they are getting this info?