If there were major tznius problems and potential arayos issues about the typical American yeshivish way of dating (as opposed to Chasidish), wouldn’t the roshei yeshiva and rabbonim, who I am sure know what goes on and are involved in their talmidim’s and children’s dating, say something and put a stop to it? If they haven’t, then maybe they feel it is necessary?
By the way, I heard from someone who grew up in and around the Mir Yeshiva, that the girls of the Mir families knew all the bochurim, and shidduchim would be arranged accordingly. So much for today’s falling standards…