We've been at DLR three times now (we usually go in early May) while there had been Grad Nites. It never felt more crowded than regular nights, and we never encountered super rowdy teens (I know others that have). Don't know if we were lucky or just did not notice.
We hit DCA in the morning and then move to DL in the afternoon or just call it an early night and go to DTD or off property for dinner. One time we planned our off property day on one of the Grad Nite days - kids can buy tickets for the whole day not just the party.